-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 GCJpcx7ItUyBLiM76RJ19WJ+5q2Go6pfT1t+xB70KxM2o+JdWjbUPXUv/RNpiTMe
 NzH9XIgL3LWpYOPRh1hnpA==

<SEC-DOCUMENT>0001365234-10-000004.txt : 20100316
<SEC-HEADER>0001365234-10-000004.hdr.sgml : 20100316
<ACCEPTANCE-DATETIME>20100316133944
ACCESSION NUMBER:		0001365234-10-000004
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100315
FILED AS OF DATE:		20100316
DATE AS OF CHANGE:		20100316

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Lazar Michael B
		CENTRAL INDEX KEY:			0001299477

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	814-00712
		FILM NUMBER:		10684810

	MAIL ADDRESS:	
		STREET 1:		C/O BLACKROCK KELSO CAPITAL CORPORATION
		STREET 2:		40 EAST 52ND STREET
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10022

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			BlackRock Kelso Capital CORP
		CENTRAL INDEX KEY:			0001326003
		IRS NUMBER:				202725151
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		40 EAST 52ND STREET
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10022
		BUSINESS PHONE:		212-754-5300

	MAIL ADDRESS:	
		STREET 1:		40 EAST 52ND STREET
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10022
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-03-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001326003</issuerCik>
        <issuerName>BlackRock Kelso Capital CORP</issuerName>
        <issuerTradingSymbol>BKCC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001299477</rptOwnerCik>
            <rptOwnerName>Lazar Michael B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O BLACKROCK KELSO CAPITAL CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>40 EAST 52ND STREET</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle>Chief Operating Officer</officerTitle>
            <otherText>C.O.O of investment adviser</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $0.001 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2010-03-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>68662</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>213049.87</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, par value $0.001 per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>40553.68</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Michael B. Lazar IRA</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, par value $0.001 per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>42493.31</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By BlackRock Kelso Capital Advisors LLC</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Restricted Shares granted by BlackRock Kelso Capital Advisors LLC (&quot;Advisor&quot;) pursuant to a Restricted Stock Agreement, dated March 15, 2010, vesting in equal installments on January 2, 2011, 2012 and 2013.</footnote>
        <footnote id="F2">Includes 6,058.56 Restricted Shares granted by Advisor pursuant to a Restricted Stock Agreement, dated December 31, 2007, vesting on January 2, 2011; and 15,781 Restricted Shares granted by Advisor pursuant to a Restricted Stock Agreement, dated January 2, 2009, vesting in equal installments on January 2, 2011 and 2012.  Excludes shares owned indirectly by a family trust.  The individual disclaims beneficial ownership of the shares owned by the trust.</footnote>
        <footnote id="F3">Includes shares owned indirectly by an individual retirement account as to which the Reporting Person is the beneficiary.</footnote>
        <footnote id="F4">The Reporting Person, as a Manager of Advisor, may be deemed to beneficially own all the Common Stock of the Issuer owned by Advisor.  The Reporting Person disclaims benefical ownership of such shares except to the extent of his pecuniary interest therein and the inclusion of such shares in this report shall not be deemed an admission of beneficial ownership of all of the reported shares for purposes of Section 16 or otherwise.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Michael B. Lazar, by Frank D. Gordon, Attorney-in-Fact</signatureName>
        <signatureDate>2010-03-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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