UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of Earliest Event Reported): May 9, 2014 (May 9, 2014)

BLACKROCK KELSO CAPITAL CORPORATION

(Exact name of registrant as specified in its charter)

40 East 52^nd Street

New York, NY 10022

(Address of principal executive offices)

(212) 810-5800

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

ITEM 5.07. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS.

Annual Meeting:

On May 9, 2014, the Registrant held its 2014 annual meeting of stockholders (the “Annual Meeting”). The proposals considered at the Annual Meeting are described in detail in the Registrant’s definitive proxy statement for the Annual Meeting as filed with the Securities and Exchange Commission on March 19, 2014 (the “Annual Meeting Proxy”). At the Annual Meeting, the Registrant’s stockholders approved the first and second proposals described in the Annual Meeting Proxy before the Annual Meeting was adjourned. As of March 12, 2014, the record date, 74,520,169 shares of common stock were eligible to vote.

First Proposal. The Registrant’s stockholders elected three directors of the Registrant (the “Class I Directors”), each of whom will serve until the 2017 annual meeting, or until his or her successor is duly elected and qualifies or until his or her earlier resignation, removal from office, death or incapacity. The Class I Directors were elected pursuant to the voting results set forth below:

Second Proposal. The Registrant’s stockholders ratified the selection of Deloitte & Touche LLP to serve as the Registrant’s independent registered public accounting firm for the year ending December 31, 2014, as set forth below:

Special Meeting:

On May 9, 2014, the Registrant held a special meeting of stockholders (the “Special Meeting”). The proposal considered at the Special Meeting are described in detail in the Registrant’s definitive proxy statement for the Special Meeting as filed with the Securities and Exchange Commission on March 19, 2014 (the “Special Meeting Proxy”). At the Special Meeting, the Registrant’s stockholders approved the proposal described in the Special Meeting Proxy before the Special Meeting was adjourned. As of March 12, 2014, the record date, 74,520,169 shares of common stock were eligible to vote.

Proposal. The Registrant’s stockholders approved a proposal to authorize flexibility for the Registrant, with approval of the Board of the Registrant, to sell or otherwise issue shares of its common stock (during the next 12 months) at a price below the Registrant’s then current net asset value per share in one or more offerings, subject to certain limitations set forth in the Special Meeting Proxy (including that the cumulative number of shares sold pursuant to such authority does not exceed 25% of the Registrant’s then outstanding common stock immediately prior to each such sale), as set forth below:

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.