-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 SgTFoPzzg2fxkskWHwqQ2jEshdcYz3lU9Xngm9gFLCo0PmTQ7d/+wKnn5Ktu7KmP
 y2i7jxdrYDAlNPVap6ut9w==

<SEC-DOCUMENT>0001140361-09-001683.txt : 20090122
<SEC-HEADER>0001140361-09-001683.hdr.sgml : 20090122
<ACCEPTANCE-DATETIME>20090122152527
ACCESSION NUMBER:		0001140361-09-001683
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20090120
FILED AS OF DATE:		20090122
DATE AS OF CHANGE:		20090122

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:		09539201

	BUSINESS ADDRESS:	
		STREET 1:		997 WANDER WAY
		CITY:			INCLINE VILLAGE
		STATE:			NV
		ZIP:			89451
		BUSINESS PHONE:		7758331811

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:		13710 FNB PARKWAY
		CITY:			OMAHA
		STATE:			NE
		ZIP:			68154-5200
		BUSINESS PHONE:		8772902772

	MAIL ADDRESS:	
		STREET 1:		13710 FNB PARKWAY
		CITY:			OMAHA
		STATE:			NE
		ZIP:			68154-5200
</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>2009-01-20</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>13710 FNB PARKWAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>OMAHA</rptOwnerCity>
            <rptOwnerState>NE</rptOwnerState>
            <rptOwnerZipCode>68154-5200</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>Deferred Share Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2009-01-20</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1233</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </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>1233</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1822</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">N/A - 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 Deferred Share Units (&quot;DSUs&quot;) 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>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Donald J. DeGrandis, Attorney for David Marshall</signatureName>
        <signatureDate>2009-01-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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