Filed Pursuant to Rule 424(b)(2)
Registration No. 333-234798

PROSPECTUS SUPPLEMENT

(To Prospectus dated January 13, 2020)

$125,000,000

OAKTREE SPECIALTY LENDING CORPORATION

Common Stock

We are a specialty finance company that looks to provide customized, one-stop credit solutions to companies with limited access to public or syndicated capital markets. We are a closed-end, externally managed, non-diversified management investment company that has elected to be regulated as a Business Development Company under the Investment Company Act of 1940, as amended. Our investment objective is to generate current income and capital appreciation by providing companies with flexible and innovative financing solutions, including first and second lien loans, unsecured and mezzanine loans, bonds, preferred equity and certain equity co-investments. We may also seek to generate capital appreciation and income through secondary investments at discounts to par in either private or syndicated transactions. We generally invest in securities that are rated below investment grade by rating agencies or that would be rated below investment grade if they were rated. Below investment grade securities, which are often referred to as “high yield” and “junk,” have predominantly speculative characteristics with respect to the issuer’s capacity to pay interest and repay principal.

Oaktree Fund Advisors, LLC, or Oaktree, serves as our investment adviser. Oaktree Fund Administration, LLC, or Oaktree Administrator, serves as our administrator. Oaktree is an affiliate of, and Oaktree Administrator is a subsidiary of, Oaktree Capital Management, L.P., a leading global investment management firm headquartered in Los Angeles, California, focused on less efficient markets and alternative investments.

We, Oaktree and Oaktree Administrator have entered into an Equity Distribution Agreement, dated February 4, 2022, with Keefe, Bruyette & Woods, Inc., JMP Securities LLC, Raymond James & Associates, Inc. and SMBC Nikko Securities America, Inc., or the Sales Agents, relating to the shares of common stock offered by this prospectus supplement and the accompanying prospectus. The Equity Distribution Agreement provides that we may offer and sell shares of our common stock having an aggregate offering price of up to $125.0 million from time to time through the Sales Agents. Sales of our common stock, if any, under this prospectus supplement and the accompanying prospectus may be made in negotiated transactions or transactions that are deemed to be “at the market,” as defined in Rule 415 under the Securities Act of 1933, as amended, including sales made directly on the Nasdaq Global Select Market or similar securities exchanges or sales made to or through a market maker other than on an exchange, at prices related to the prevailing market prices or at negotiated prices.

Pursuant to the Equity Distribution Agreement, the Sales Agents will receive a commission from us of up to 1.50% of the gross sales price of any shares of our common stock sold through the Sales Agents. The Sales Agents are not required to sell any specific number or dollar amount of common stock but will use their commercially reasonable efforts consistent with their normal sales and trading practices to sell the shares of our common stock offered by this prospectus supplement and the accompanying prospectus. See “Plan of Distribution” beginning on page S-14 of this prospectus supplement. The sales price per share of our common stock offered by this prospectus supplement and the accompanying prospectus, less commissions payable under the Equity Distribution Agreement and discounts, if any, will not be less than the net asset value per share of our common stock at the time of such sale unless we have stockholder approval to issue common stock at prices below net asset value.

Our common stock is traded on the Nasdaq Global Select Market under the symbol “OCSL”. The last reported closing price for our common stock on February 4, 2022 was $7.68 per share. The net asset value of our common stock as of December 31, 2021 (the last date prior to the date of this prospectus supplement on which we determined net asset value) was $7.34 per share.

Shares of closed-end investment companies, including Business Development Companies, frequently trade at a discount to their net asset value. If our shares trade at a discount to our net asset value, it will likely increase the risk of loss for purchasers in this offering. An investment in our common stock involves certain risks, including, among other things, the risk of leverage and risks relating to investments in securities of small, private and developing companies. You should review carefully the risks and uncertainties, including the risk of leverage, described in the section titled “Risk Factors” beginning on page 5 of the accompanying prospectus or otherwise included in or incorporated by reference herein or the accompanying prospectus and in any free writing prospectuses we have authorized for use in connection with a specific offering, and under similar headings in the other documents that are incorporated by reference into this prospectus supplement and the accompanying prospectus before investing in our securities.

This prospectus supplement, the accompanying prospectus, any free writing prospectus and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus contain important information about us that a prospective investor should know before investing in our common stock. Please read this prospectus supplement, the accompanying prospectus, any free writing prospectus and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus before investing and keep them for future reference. We file periodic reports, current reports, proxy statements and other information with the Securities and Exchange Commission. You may obtain this information free of charge or make an investor inquiry by contacting us at 333 South Grand Ave., 28th Floor, Los Angeles, CA 90071 or by calling us collect at (213) 830-6300 or on our website at oaktreespecialtylending.com. Except for the documents incorporated by reference into this prospectus supplement or the accompanying prospectus, information on our website is not incorporated into or a part of this prospectus supplement or the accompanying prospectus. The Securities and Exchange Commission also maintains a website at www.sec.gov that contains such information.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Prospectus Supplement dated February 7, 2022.

TABLE OF CONTENTS

PROSPECTUS SUPPLEMENT

PROSPECTUS

ABOUT THIS PROSPECTUS SUPPLEMENT

You should rely only on the information contained in this prospectus supplement, the accompanying prospectus, any free writing prospectus, and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus, or any other information to which we have referred you when considering whether to purchase any securities offered by this prospectus supplement. We have not, and the Sales Agents have not, authorized any other person to provide you with different or additional information from that contained in this prospectus supplement, the accompanying prospectus, or any free writing prospectus. We are not, and the Sales Agents are not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted.

This document is in two parts. The first part is this prospectus supplement, which describes the terms of this offering and also adds to and updates information contained in the accompanying prospectus. The second part is the accompanying prospectus, which gives more general information and disclosure. To the extent the information contained in this prospectus supplement differs from the information contained in the accompanying prospectus, the information in this prospectus supplement shall control. The information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus is accurate as of their respective dates. Our financial condition, results of operations and prospects may have changed since that date. To the extent required by law, we will amend or supplement the information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus to reflect any material changes to such information subsequent to the date of this prospectus supplement and the accompanying prospectus and prior to the completion of this offering.

S-i

S-1

S-2

S-3

S-4

S-5

S-6

FEES AND EXPENSES

The following table is intended to assist you in understanding the costs and expenses that an investor in shares of our common stock will bear directly or indirectly. We caution you that some of the percentages indicated in the table below are estimates and may vary. Except where the context suggests otherwise, whenever this prospectus supplement contains a reference to fees or expenses paid by “you” or “us”, or that “we” will pay fees or expenses, our common stockholders will indirectly bear such fees or expenses. Such expenses also include those of our consolidated subsidiaries.

S-7

Under the Investment Advisory Agreement, the second part of the incentive fee (the “capital gains incentive fee”) is determined and payable in arrears as of the end of each fiscal year (or upon termination of the Investment Advisory Agreement, as of the termination date) commencing with the fiscal year ended September 30, 2019 and equals 17.5% of our realized capital gains, if any, on a cumulative basis from the beginning of the fiscal year ended September 30, 2019 through the end of each fiscal year, computed net of all realized capital losses and unrealized capital depreciation on a cumulative basis, less the aggregate amount of any previously paid capital gains incentive fees under the Investment Advisory Agreement. Any realized capital gains or losses and unrealized capital depreciation with respect to our portfolio as of the end of the fiscal year ended September 30, 2018 are excluded from the calculations of the second part of the incentive fee. In addition, the calculation of realized capital gains, realized capital losses and unrealized capital depreciation does (1) not include any such amounts resulting solely from merger-related accounting adjustments in connection with the assets acquired in the Mergers, including any premium or discount paid for the acquisition of such assets, solely to the extent that the inclusion of such merger-related accounting adjustments, in the aggregate, would result in an increase in the capital gains incentive fee and (2) include any such amounts associated with the investments acquired in the Mergers for the period from October 1, 2018 to the date of closing of the Mergers, solely to the extent that the exclusion of such amounts, in the aggregate, would result in an increase in the capital gains incentive fee. See “Item 1. Business – Investment Advisory Agreement – Management and Incentive Fee” in our most recent Annual Report on Form 10-K and incorporated by reference herein.

The incentive fee referenced in the table above is based on annualized actual amounts of the incentive fee on income incurred during the three months ended December 31, 2021 annualized for a full year, and the capital gains incentive fee payable under the Investment Advisory Agreement as of September 30, 2021, the last date prior to the date of this prospectus on which such fee was payable under the terms of the Investment Advisory Agreement.

S-8

Example

The following example demonstrates the projected dollar amount of total cumulative expenses that would be incurred over various periods with respect to a hypothetical investment in our common stock assuming that we hold no cash or liabilities other than debt. In calculating the following expense amounts, we have assumed that our annual operating expenses remain at the levels set forth in the table above. These amounts assume (1) a 1.50% sales load (Sales Agents discounts and commissions) and (2) offering expenses totaling 0.32%.

The example and the expenses in the tables above should not be considered a representation of our future expenses, and actual expenses may be greater or less than those shown. While the example assumes, as required by the SEC, a 5% annual return, our performance will vary and may result in a return greater or less than 5%. The incentive fee based on pre-incentive fee net investment income under the Investment Advisory Agreement, which, assuming a 5% annual return, would either not be payable or would have an insignificant impact on the expense amounts shown above, is not included in the example. If we achieve sufficient returns on our investments, including through the realization of capital gains, to trigger a greater incentive fee, our expenses, and returns to our investors, would be higher. For purposes of this example, we have assumed that as of October 1, 2021, the sum of our realized capital losses and unrealized capital depreciation on a cumulative basis since October 1, 2018 equaled zero. In addition, while the example assumes reinvestment of all distributions at net asset value, participants in our dividend reinvestment plan will receive a number of shares of our common stock, determined by dividing the total dollar amount of the cash distribution payable to a participant by either (i) the greater of (a) the current net asset value per share of our common stock and (b) 95% of the market price per share of our common stock at the close of trading on the payment date fixed by our Board of Directors in the event that we use newly issued shares to satisfy the share requirements of the dividend reinvestment plan or (ii) the average purchase price, excluding any brokerage charges or other charges, of all shares of common stock purchased by the administrator of the dividend reinvestment plan in the event that shares are purchased in the open market to satisfy the share requirements of the dividend reinvestment plan, which may be at, above or below net asset value. See “Dividend Reinvestment Plan” in the accompanying prospectus for more information.

S-9

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

Some of the statements in this prospectus supplement and the accompanying prospectus constitute forward-looking statements because they relate to future events or our future performance or financial condition. The forward-looking statements contained in this prospectus supplement and the accompanying prospectus may include statements as to:

In addition, words such as “anticipate,” “believe,” “expect,” “seek,” “plan,” “should,” “estimate,” “project,” and “intend” indicate forward-looking statements, although not all forward-looking statements include these words. The forward-looking statements contained in this prospectus supplement and the accompanying prospectus, involve risks and uncertainties. Our actual results could differ materially from those implied or expressed in the forward-looking statements for any reason, including the factors set forth in “Risk Factors” in the accompanying prospectus and documents incorporated by reference in this prospectus supplement and the accompanying prospectus. Other factors that could cause actual results to differ materially include:

We have based the forward-looking statements included in this prospectus supplement and the accompanying prospectus on information available to us on the date of this prospectus supplement and the accompanying prospectus, as appropriate, and we assume no obligation to update any such forward-looking statements, except as required by law. Although we undertake no obligation to revise or update any forward-looking statements, whether as a result of new information, future events or otherwise, you are advised to consult any additional disclosures that we may make directly to you or through reports that we in the future may file with the SEC, including annual reports on Form 10-K, quarterly reports on Form 10-Q and current reports on

S-10

Form 8-K. The forward-looking statements contained in this prospectus supplement and the accompanying prospectus are excluded from the safe harbor protection provided by Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and the forward looking statements contained in our periodic reports are excluded from the safe-harbor protection provided by Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act.

S-11

USE OF PROCEEDS

Sales of our common stock, if any, under this prospectus supplement and the accompanying prospectus may be made in negotiated transactions or transactions that are deemed to be “at the market,” as defined in Rule 415 under the Securities Act, including sales made directly on the Nasdaq Global Select Market or similar securities exchanges or sales made to or through a market maker other than on an exchange, at prices related to the prevailing market prices or at negotiated prices. There is no guarantee that there will be any sales of our common stock pursuant to this prospectus supplement and the accompanying prospectus. Actual sales, if any, of our common stock under this prospectus supplement and the accompanying prospectus may be less than as set forth in this paragraph depending on, among other things, the market price of our common stock at the time of any such sale. As a result, the actual net proceeds we receive may be more or less than the amount of net proceeds estimated in this prospectus supplement. However, the sales price per share of our common stock offered by this prospectus supplement and the accompanying prospectus, less commissions payable under the Equity Distribution Agreement, will not be less than the net asset value per share of our common stock at the time of such sale unless we have stockholder approval to issue common stock at prices below net asset value. If we sell shares of our common stock with an aggregate offering price of $125.0 million, we anticipate that our net proceeds, after deducting the Sales Agents’ commissions and estimated expenses payable by us, will be approximately $122.7 million.

We intend to use the net proceeds from the sale of our common stock to invest in portfolio companies in accordance with our investment objectives and strategies and for general corporate purposes. We may also use a portion of the net proceeds from this offering to repay amounts outstanding under our existing credit facilities and to pay operating expenses.

As of December 31, 2021, we had $495.0 million of borrowings outstanding under the Syndicated Credit Facility. Our borrowings under the Syndicated Credit Facility bore interest at a weighted average interest rate of 2.174% for the three months ended December 31, 2021. As of December 31, 2021, (i) the period during which we may make drawings under the Syndicated Credit Facility will expire on May 4, 2025 and the maturity date is May 4, 2026 and (ii) the interest rate margin for (a) LIBOR loans (which may be 1-, 2-, 3- or 6-month, at our option) was 2.00% and (b) alternate base rate loans was 1.00%. As of December 31, 2021, we had $155.0 million outstanding under the Citibank Facility. Our borrowings under the Citibank Facility bore interest at a weighted average interest rate of 1.830% for the three months ended December 31, 2021. As of December 31, 2021, borrowings under the Citibank Facility are subject to certain customary advance rates and accrue interest at a rate equal to LIBOR plus between 1.25% and 2.20% per annum on broadly syndicated loans, subject to observable market depth and pricing, and LIBOR plus 2.25% per annum on all other eligible loans during the reinvestment period. In addition, as of December 31, 2021, for the duration of the reinvestment period there is a non-usage fee payable of 0.50% per annum on the undrawn amount under the Citibank Facility. As of December 31, 2021, the reinvestment period under the Citibank Facility is scheduled to expire on November 18, 2023 and the maturity date is November 18, 2024. To the extent we use net proceeds from this offering to repay amounts under our existing credit facilities, we intend to subsequently reborrow such amounts.

Certain proceeds of this offering may be used to repay outstanding indebtedness under the Syndicated Credit Facility. Accordingly, certain of the Sales Agents may receive more than 5% of the proceeds of this offering to the extent such proceeds are used to repay or repurchase outstanding indebtedness under the Syndicated Credit Facility. In addition, in the future, the Sales Agents or their affiliates may be lenders under other credit facilities to which we are from time to time party.

S-12

CAPITALIZATION

The following table sets forth our capitalization as of December 31, 2021.

S-13

PLAN OF DISTRIBUTION

Keefe, Bruyette & Woods, Inc., JMP Securities LLC, Raymond James & Associates, Inc. and SMBC Nikko Securities America, Inc. are acting as Sales Agents in connection with the offer and sale of shares of our common stock pursuant to this prospectus supplement and the accompanying prospectus. Upon written instructions from us, the Sales Agents will use their commercially reasonable efforts consistent with their normal sales and trading practices to sell, as our Sales Agents, our common stock under the terms and subject to the conditions set forth in the Equity Distribution Agreement dated February 4, 2022. We will instruct the Sales Agents as to the amount of common stock to be sold by them. We may instruct the Sales Agents not to sell common stock if the sales cannot be effected at or above the price designated by us in any instruction. The sales price per share of our common stock offered by this prospectus supplement and the accompanying prospectus, less commissions payable under the Equity Distribution Agreement and discounts, if any, will not be less than the net asset value per share of our common stock at the time of such sale unless we have stockholder approval to issue common stock at prices below net asset value. We or the Sales Agents may suspend the offering of shares of our common stock upon proper notice and subject to other conditions.

Sales of our common stock, if any, under this prospectus supplement and the accompanying prospectus may be made in negotiated transactions or transactions that are deemed to be “at the market,” as defined in Rule 415 under the Securities Act, including sales made directly on the Nasdaq Global Select Market or similar securities exchanges or sales made to or through a market maker other than on an exchange, at prices related to the prevailing market prices or at negotiated prices.

The Sales Agents will provide written confirmation of a sale to us no later than the opening of the trading day on the Nasdaq Global Select Market following each trading day in which shares of our common stock are sold under the Equity Distribution Agreement. Each confirmation will include the number of shares of common stock sold on the preceding day, the net proceeds to us and the compensation payable by us to the Sales Agents, in connection with the sales.

Pursuant to the Equity Distribution Agreement, the Sales Agents will receive a commission from us of up to 1.50% of the gross sales price of any shares of our common stock sold through the Sales Agents. We estimate that the total expenses for the offering, excluding compensation payable to the Sales Agents under the terms of the Equity Distribution Agreement, will be approximately $0.4 million, which includes an aggregate of $40,000 in reimbursement of reasonable fees and expenses of counsel to the Sales Agents incurred in connection with the initial launch of this offering and up to $7,500 per calendar quarter during the term of the Equity Distribution Agreement for fees and expenses of counsel to the Sales Agents incurred in connection with quarterly updates for this offering.

Settlement for sales of shares of common stock will occur on the second trading day following the date on which such sales are made, or on some other date that is agreed upon by us and the Sales Agents in connection with a particular transaction, in return for payment of the net proceeds to us. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

We will report, through our quarterly reports on Form 10-Q and annual reports on Form 10-K, the number of shares of our common stock sold through the Sales Agents under the Equity Distribution Agreement, the net proceeds to us and compensation payable by us to the Sales Agents with regard to shares sold pursuant to the Equity Distribution Agreement.

In connection with the sale of the common stock on our behalf, each Sales Agent may be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation of each Sales Agent may be deemed to be underwriting commissions or discounts. We have agreed to provide indemnification and contribution to the Sales Agents against certain civil liabilities, including liabilities under the Securities Act.

S-14

The offering of our shares of common stock pursuant to the Equity Distribution Agreement will terminate upon the earlier of (i) the sale of all common stock subject to the Equity Distribution Agreement or (ii) the termination of the Equity Distribution Agreement. The Equity Distribution Agreement may be terminated by us in our sole discretion under the circumstances specified in the Equity Distribution Agreement by giving notice to the Sales Agents. In addition, the Sales Agents may terminate the Equity Distribution Agreement under the circumstances specified in the Equity Distribution Agreement by giving notice to us.

The principal business addresses of the Sales Agents are: Keefe, Bruyette & Woods, Inc., 787 7th Avenue, 4th Floor, New York, NY 10019; JMP Securities LLC, 600 Montgomery Street, 11th Floor, San Francisco, CA 94111; Raymond James & Associates, Inc., 880 Carillon Parkway, St. Petersburg, FL 33716; and SMBC Nikko Securities America, Inc., 277 Park Avenue, New York, NY 10172.

Passive Market Making

In connection with this offering, the Sales Agents may engage in passive market making transactions in the common stock on The Nasdaq Global Select Market in accordance with Rule 103 of Regulation M under the Exchange Act during a period before the commencement of offers or sales of common stock and extending through the completion of distribution. A passive market maker must display its bid at a price not in excess of the highest independent bid of that security. However, if all independent bids are lowered below the passive market maker’s bid, that bid must then be lowered when specified purchase limits are exceeded. Passive market making may cause the price of our common stock to be higher than the price that otherwise would exist in the open market in the absence of those transactions. The Sales Agents are not required to engage in passive market making and may end passive market making activities at any time.

Nasdaq Global Select Market Listing

Our common stock is listed on The Nasdaq Global Select Market under the symbol “OCSL.”

Other Relationships

The Sales Agents and their respective affiliates are full service financial institutions engaged in various activities, which may include sales and trading, commercial and investment banking, advisory, investment management, investment research, principal investment, hedging, market making, brokerage and other financial and non-financial activities and services. The Sales Agents and their respective affiliates have, from time to time, performed, and may in the future perform, various financial advisory and investment banking services for us and our affiliates, for which they received or will receive customary fees and expenses, including acting as sales agents for our and our affiliates’ securities offerings.

In the ordinary course of their various business activities, the Sales Agents and their respective affiliates, officers, directors and employees may purchase, sell or hold a broad array of investments and actively trade securities, derivatives, loans, commodities, currencies, credit default swaps and other financial instruments for their own account and for the accounts of their customers, and such investment and trading activities may involve or relate to assets, securities and/or instruments of ours and our affiliates (directly, as collateral securing other obligations or otherwise) and/or persons and entities with relationships with us and our affiliates. If the Sales Agents or their respective affiliates have a lending relationship with us, the Sales Agents or their respective affiliates routinely hedge, or may hedge, their credit exposure to us consistent with their customary risk management policies. Typically, the Sales Agents and their respective affiliates would hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities, including potentially the common stock offered hereby. Any such credit default swaps or short positions could adversely affect future trading prices of the common stock offered hereby. The Sales Agents and their respective affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of such assets, securities or

S-15

instruments and may at any time hold, or recommend to clients that they should acquire, long and/or short positions in such assets, securities and instruments.

Certain proceeds of this offering may be used to repay outstanding indebtedness under the Syndicated Credit Facility. Affiliates of certain of the Sales Agents are lenders under the Syndicated Credit Facility. Accordingly, affiliates of certain of the Sales Agents may receive more than 5% of the proceeds of this offering to the extent such proceeds are used to repay or repurchase outstanding indebtedness under the Syndicated Credit Facility. In addition, in the future, the Sales Agents or their affiliates may be lenders under other credit facilities to which we are from time to time party.

Other Jurisdictions

Other than in the United States, no action has been taken by us or the Sales Agents that would permit a public offering of the securities offered by this prospectus supplement in any jurisdiction where action for that purpose is required. The securities offered by this prospectus supplement may not be offered or sold, directly or indirectly, nor may this prospectus supplement or any other offering material or advertisements in connection with the offer and sale of any such securities be distributed or published in any jurisdiction, except under circumstances that will result in compliance with the applicable rules and regulations of that jurisdiction. Persons into whose possession this prospectus supplement comes are advised to inform themselves about and to observe any restrictions relating to the offering and the distribution of this prospectus supplement. This prospectus supplement does not constitute an offer to sell or a solicitation of an offer to buy any securities offered by this prospectus supplement in any jurisdiction in which such an offer or a solicitation is unlawful.

S-16

LEGAL MATTERS

The validity of the common stock offered hereby and certain legal matters for us in connection with the offering will be passed upon for us by Proskauer Rose LLP, Washington, D.C. Certain legal matters in connection with the offering will be passed upon for the Sales Agents by Dechert LLP, Washington, D.C.

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

This prospectus supplement is part of a registration statement that we have filed with the SEC. We are allowed to “incorporate by reference” the information that we file with the SEC, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus supplement, and later information that we file with the SEC will automatically update and supersede this information.

We previously filed the following documents with the SEC, and such filings are incorporated by reference into this prospectus supplement:

We also incorporate by reference into this prospectus additional documents that we may file with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act from the filing of this prospectus supplement until all of the securities offered by this prospectus supplement have been sold or we otherwise terminate the offering of these securities, including all filings made after the date of the initial filing of the registration statement of which this prospectus is a part and prior to the effectiveness of the registration statement; provided, however, that information “furnished” under Item 2.02 or Item 7.01 of Form 8-K or other information “furnished” to the SEC which is not deemed filed is not incorporated by reference in this prospectus supplement and the accompanying prospectus. Information that we subsequently file with the SEC will automatically update and may supersede information in this prospectus supplement, the accompanying prospectus and information previously filed with the SEC.

These filings may also be accessed on our website at www.oaktreespecialtylending.com. Except for documents incorporated by reference into this prospectus supplement and the accompanying prospectus, information contained on our website is not incorporated by reference into this prospectus supplement. You may also request a copy of these filings (other than exhibits, unless the exhibits are specifically incorporated by reference into these documents) at no cost by writing, emailing or calling Investor Relations at the following address and telephone number:

Investor Relations

Oaktree Specialty Lending Corporation

1301 Avenue of the Americas, 34th Floor

New York, NY 10019

(212) 284-1900

ocsl-ir@oaktreecapital.com

S-17

$1,000,000,000

Oaktree Specialty Lending Corporation

Common Stock

Debt Securities

Warrants

Subscription Rights

We are a specialty finance company that looks to provide customized, one-stop credit solutions to companies with limited access to public or syndicated capital markets. We were formed in late 2007 and operate as a closed-end, externally managed, non-diversified management investment company that has elected to be regulated as a Business Development Company under the Investment Company Act, of 1940, as amended. We seek to generate current income and capital appreciation by providing companies with flexible and innovative financing solutions, including first and second lien loans, unsecured and mezzanine loans, bonds, preferred equity and certain equity co-investments. We may also seek to generate capital appreciation and income through secondary investments at discounts to par in either private or syndicated transactions. We generally invest in securities that are rated below investment grade by rating agencies or that would be rated below investment grade if they were rated. Below investment grade securities, which are often referred to as “high yield” and “junk,” have predominantly speculative characteristics with respect to the issuer’s capacity to pay interest and repay principal.

We may offer, from time to time in one or more offerings, up to $1,000,000,000 of shares of our common stock, debt securities, warrants representing rights to purchase common stock or debt securities or subscription rights to purchase common stock, which we refer to, collectively, as the “securities.” Our securities may be offered at prices and on terms to be disclosed in one or more supplements to this prospectus. You should read this prospectus, the applicable prospectus supplement and any free writing prospectuses carefully before you invest in our securities.

Our securities may be offered directly to one or more purchasers, including existing stockholders in a rights offering, through agents designated from time to time by us, or to or through underwriters or dealers. The prospectus supplement relating to an offering will identify any agents or underwriters involved in the sale of our securities, and will disclose any applicable purchase price, fee, commission or discount arrangement between us and our agents or underwriters or among our underwriters or the basis upon which such amount may be calculated. See “Plan of Distribution.” We may not sell any of our securities through agents, underwriters or dealers without delivery of a prospectus supplement describing the method and terms of the offering of such securities.

Our common stock is traded on the Nasdaq Global Select Market under the symbol “OCSL.” On November 19, 2019 and September 30, 2019, the last reported sale price of our common stock was $5.28 and $5.18 per share, respectively. Our Board of Directors is required to determine the net asset value per share of our common stock on a quarterly basis. Our net asset value per share of our common stock as of September 30, 2019 was $6.60.

An investment in our securities involves certain risks, including, among other things, the risk of leverage and risks relating to investments in securities of small, private and developing businesses. Shares of closed-end investment companies frequently trade at a discount to their net asset value per share. If our shares trade at a discount to their net asset value, this will likely increase the risk of loss to purchasers of our common stock. You should review carefully the risks and uncertainties, including the risk of leverage and dilution, described in the section titled “Risk Factors” beginning on page 5 of this prospectus or otherwise incorporated by reference herein and included in, or incorporated by reference into, the applicable prospectus supplement and in any free writing prospectuses we have authorized for use in connection with a specific offering, and under similar headings in the other documents that are incorporated by reference into this prospectus before investing in our securities.

This prospectus and any accompanying prospectus supplement contain important information about us that a prospective investor should know before investing in our securities. Please read this prospectus and any accompanying prospectus supplement before investing and keep them for future reference. We file periodic reports, current reports, proxy statements and other information with the Securities and Exchange Commission. This information is available free of charge by contacting us at 333 South Grand Ave., 28th Floor, Los Angeles, CA 90071 or by calling us collect at (213) 830-6300 or on our website at oaktreespecialtylending.com. Except for the documents incorporated by reference into this prospectus, information on our website is not incorporated into or a part of this prospectus or any related prospectus supplement. The Securities and Exchange Commission also maintains a website at www.sec.gov that contains such information.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Prospectus dated January 13, 2020

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we have filed with the Securities and Exchange Commission, or SEC, using the “shelf” registration process. Under the shelf registration process, we may offer, from time to time, up to $1,000,000,000 of our securities on terms to be determined at the time of the offering. This prospectus provides you with a general description of the securities that we may offer. Each time we use this prospectus to offer securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. The prospectus supplement may also add, update or change information contained or incorporated by reference in this prospectus. Please carefully read this prospectus, any accompanying prospectus supplement, any free writing prospectus and the documents incorporated by reference in this prospectus and any accompanying prospectus supplement.

No dealer, salesperson or other person is authorized to give any information or to represent anything not contained or incorporated by reference in this prospectus or any accompanying supplement to this prospectus. You must not rely on any unauthorized information or representations not contained or incorporated by reference in this prospectus or any accompanying prospectus supplement as if we had authorized it. This prospectus and any accompanying prospectus supplement do not constitute an offer to sell or a solicitation of any offer to buy any security other than the registered securities to which they relate, nor do they constitute an offer to sell or a solicitation of an offer to buy any securities in any jurisdiction to any person to whom it is unlawful to make such an offer or solicitation in such jurisdiction. The information contained or incorporated by reference in this prospectus and any accompanying prospectus supplement is accurate as of their respective dates. Our financial condition, results of operations and prospects may have changed since that date. To the extent required by law, we will amend or supplement the information contained or incorporated by reference in this prospectus and any accompanying prospectus supplement to reflect any material changes to such information subsequent to the date of the prospectus and any accompanying prospectus supplement and prior to the completion of any offering pursuant to the prospectus and any accompanying prospectus supplement.

i

1

2

3

4

RISK FACTORS

An investment in any securities offered pursuant to this prospectus and any accompanying prospectus supplement involves substantial risks. You should carefully consider the risk factors incorporated by reference herein from our most recent Annual Report on Form 10-K and our subsequent Quarterly Reports on Form 10-Q and the other information contained in this prospectus, as updated, amended or superseded by our subsequent filings under the Securities Exchange Act of 1934, as amended, or the Exchange Act, and the risk factors and other information contained in any accompanying prospectus supplement or free writing prospectus before acquiring any of such securities. The occurrence of any of these risks could materially and adversely affect our business, prospects, financial condition, results of operations and cash flow and might cause you to lose all or part of your investment in the offered securities. The risks described in these documents are not the only risks we face, and there may be additional risks that we do not presently know of or that we currently consider not likely to have a significant impact. New risks may emerge at any time and we cannot predict such risks or estimate the extent to which they may affect our business or our financial performance.

5

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

Some of the statements in this prospectus and any accompanying prospectus supplement constitute forward-looking statements because they relate to future events or our future performance or financial condition. The forward-looking statements contained in this prospectus and any accompanying prospectus supplement may include statements as to:

In addition, words such as “anticipate,” “believe,” “expect,” “seek,” “plan,” “should,” “estimate,” and “intend” indicate forward-looking statements, although not all forward-looking statements include these words. The forward-looking statements contained in this prospectus, and any accompanying prospectus supplement, involve risks and uncertainties. Our actual results could differ materially from those implied or expressed in the forward-looking statements for any reason, including the factors set forth in “Risk Factors” and elsewhere in this prospectus and any accompanying prospectus supplement. Other factors that could cause actual results to differ materially include:

We have based the forward-looking statements included in this prospectus and will base the forward-looking statements included in any accompanying prospectus supplement on information available to us on the date of this prospectus and any accompanying prospectus supplement, as appropriate, and we assume no obligation to update any such forward-looking statements, except as required by law. Although we undertake no obligation to revise or update any forward-looking statements, whether as a result of new information, future events or otherwise, you are advised to consult any additional disclosures that we may make directly to you or through reports that we in the future may file with the SEC, including annual reports on Form 10-K, quarterly reports on Form 10-Q and current reports on Form 8-K. The forward-looking statements contained in this prospectus and any accompanying prospectus supplement are excluded from the safe harbor protection provided by Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and the forward looking statements contained in our periodic reports are excluded from the safe-harbor protection provided by Section 21E of the Exchange Act.

6

USE OF PROCEEDS

We intend to use substantially all of the net proceeds from selling our securities to make investments in accordance with our investment objective and strategies described in this prospectus or any prospectus supplement and for general corporate purposes. We may also use a portion of the net proceeds to reduce any of our outstanding borrowings, including borrowings under the Credit Facility and to redeem or repurchase the 2024 Notes and 2028 Notes.

We anticipate that substantially all of the net proceeds from any offering of our securities will be used as described above within three to six months. Pending such use, we will invest the net proceeds primarily in high quality, short-term debt securities consistent with our business development company election and our election to be taxed as a RIC. Our ability to achieve our investment objective may be limited to the extent that the net proceeds from an offering, pending full investment, are held in interest-bearing deposits or other short-term instruments. The prospectus supplement relating to an offering will more fully identify the use of proceeds from any offering.

7

PORTFOLIO COMPANIES

The following table sets forth certain information as of September 30, 2019, for each portfolio company in which we had a debt or equity investment. Our only formal relationships with our portfolio companies are the managerial assistance ancillary to our investments and the board observation or participation rights we may receive. For example, certain of our officers may serve as members of the boards of certain of our portfolio companies.

8

9

10

11