UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE

SECURITIES EXCHANGE ACT OF 1934

Filed by the Registrant  ☒

Filed by a Party other than the Registrant  ☐

Check the appropriate box:

Oaktree Specialty Lending Corporation

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

YOUR VOTE IS VERY IMPORTANT Our Board of Directors recommends that you respond to this solicitation by voting FOR the proposal described in the accompanying proxy statement. Dear Stockholder, We are pleased to invite you to participate at the Special Meeting of Stockholders of Oaktree Specialty Lending Corporation (“OCSL”), to be held virtually on March 17, 2023 at 10:00 a.m. Pacific Time (1:00 p.m., Eastern Time) at the following website: www.virtualshareholdermeeting.com/ocsl2023sm. Enclosed are the proxy materials, which describe the proposal to be considered at the meeting in detail. We kindly request that you review these materials and cast your vote by proxy in advance of the meeting date to ensure that a quorum is achieved. At the meeting, you will be asked to consider and vote on a proposal to authorize the Company, with the approval of the Board of Directors, to sell or otherwise issue shares of its common stock at a price below its then current net asset value (“NAV”) per share, provided that the number of shares issued does not exceed 25% of its then outstanding common stock. While OCSL has no immediate plans to issue any shares of its common stock future to issue shares of its common stock below NAV per share, which typically must be undertaken quickly. Your vote and participation are very important to us, no matter how many or few shares in OCSL you own. the enclosed proxy materials carefully and vote your shares using any one of the methods described below. Your prompt response will help us meet stockholder approval requirements before the meeting, thereby reducing the risk of postponement and additional solicitation costs. If you have any questions about voting, please call our proxy solicitor, Broadridge, at 1-844-557-9030. Thank you for your continued support of OCSL. Sincerely, Armen Panossian Mathew Pendo President FOUR WAYS TO VOTE ONLINE PHONE QR CODE MAIL WWW.PROXYVOTE.COM WITH A PROXY CARD WITH A SMARTPHONE VOTE PROCESSING PROXY QUESTIONS? Please have your proxy card in hand Call 1-800-690-6903 with Vote by scanning the Mark, sign and date Call 1-844-557-9030 when accessing the website. There a touch-tone phone to vote Quick Response Code or your ballot and return are easy-to-follow directions to using an automated system. “QR Code” on the Proxy it in the postage-paid help you complete the electronic Card/VIF enclosed. envelope provided. voting instruction form. S37865-LTR

Your vote is important—please vote your shares today. The Oaktree Specialty Lending Corporation special meeting will be held on March 17, 2023. Whether or not you plan to attend, your vote is very important. You can vote your shares by internet, telephone, QR code, or mail. Simply follow the instructions on the enclosed form. For your convenience, we’ve highlighted where you can find your unique Control Number. If you have any questions or need assistance, please call 1-844-557-9030. FOUR WAYS TO VOTE ONLINE PHONE QR CODE MAIL WWW.PROXYVOTE.COM WITHOUT A PROXY CARD WITH A SMARTPHONE VOTE PROCESSING Please have your proxy card in Call 1-844-557-9030 Vote by scanning the Mark, sign and date hand when accessing the website. Monday to Friday, 9:00 a.m. Quick Response Code or your ballot and return There are easy-to-follow directions to 9:00 p.m. ET to speak with “QR Code” on the Proxy it in the postage-paid to help you complete the electronic a proxy specialist. Card/VIF enclosed. envelope provided. voting instruction form. WITH A PROXY CARD Call 1-800-690-6903 with a touch-tone phone to vote using an automated system.