-----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,
 LfmTyCHNBg9YsbQj+PFOXMQQTZ8T6Ws+hs27mbNkh+hb/35lotlwv0sewZiF0+Qj
 X3TZ8itsvNO3CscztiBbtg==

<SEC-DOCUMENT>0001140361-10-006605.txt : 20100216
<SEC-HEADER>0001140361-10-006605.hdr.sgml : 20100215
<ACCEPTANCE-DATETIME>20100216161042
ACCESSION NUMBER:		0001140361-10-006605
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100212
FILED AS OF DATE:		20100216
DATE AS OF CHANGE:		20100216

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			MARSHALL DAVID
		CENTRAL INDEX KEY:			0001208444

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-26091
		FILM NUMBER:		10607825

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TC PIPELINES LP
		CENTRAL INDEX KEY:			0001075607
		STANDARD INDUSTRIAL CLASSIFICATION:	NATURAL GAS TRANSMISSION [4922]
		IRS NUMBER:				522135448
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		717 TEXAS STREET, SUITE #2400
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77002
		BUSINESS PHONE:		(877) 290-2772

	MAIL ADDRESS:	
		STREET 1:		717 TEXAS STREET, SUITE #2400
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77002
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-02-12</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001075607</issuerCik>
        <issuerName>TC PIPELINES LP</issuerName>
        <issuerTradingSymbol>TCLP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001208444</rptOwnerCik>
            <rptOwnerName>MARSHALL DAVID</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>717 TEXAS STREET, SUITE #2400</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77002</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Distribution Equivalent Rights for Deferred Share Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-02-12</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>55</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common units representing limited p/ship interests</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>55</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2841</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">N/A - The distribution equivalent rights accrued on the number of Deferred Share Units (&quot;DSUs&quot;) recorded in his account.  Each distribution equivalent right is the economic equivalent of one DSU.  Upon termination of board service, Common Units representing limited partnership interests may be purchased on the open market on behalf of Mr. Marshall whereby he would receive Common Units in a number equal to the number of DSUs recorded in his account less any applicable withholdings. Alternatively, Mr. Marshall may elect to receive the value of his DSU entitlement in cash.  The cash payment amount shall be determined by multiplying the number of DSUs recorded in his account by the Fair Market Value of a Common Unit less any applicable withholdings.</footnote>
        <footnote id="F2">N/A - the DSUs are fully vested and are redeemable only following Mr. Marshall's termination of Board service.</footnote>
        <footnote id="F3">The distribution amount reflects the number of DSUs added to the director's share unit account as of the record date for the distribution.  Pursuant to the Share Unit Plan for Non-Employee Directors (2007), the distribution amount is calculated based on the declared distribution multiplied by the number of share units in the account, divided by the market value of the common units on the payment date for such distribution.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Annie C. Belecki, Attorney for David Marshall</signatureName>
        <signatureDate>2010-02-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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