<?xml version="1.0"?>

<ownershipDocument>

    <documentType>4</documentType>

    <periodOfReport>2003-01-15</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000078460</issuerCik>
        <issuerName>PIEDMONT NATURAL GAS CO INC</issuerName>
        <issuerTradingSymbol>PNY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001238169</rptOwnerCik>
            <rptOwnerName>RUSSELL DONALD S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

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        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>
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        </transactionDate>
        <deemedExecutionDate>
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        </deemedExecutionDate>
        <transactionCoding>
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            <equitySwapInvolved>0</equitySwapInvolved>
            <footnoteId id="F1"/>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
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            </transactionShares>
            <transactionValue>
                <value>35.14</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
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            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>67647.586</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

    <nonDerivativeSecurity>
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        </securityTitle>
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        </deemedExecutionDate>
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        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
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                <value>19.763</value>
            </transactionShares>
            <transactionValue>
                <value>33.75</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
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            </transactionAcquiredDisposedCode>
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                <value>67667.349</value>
            </sharesOwnedFollowingTransaction>
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            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

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        </deemedExecutionDate>
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    </nonDerivativeSecurity>

    <nonDerivativeSecurity>
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            <value>Common Stock</value>
        </securityTitle>
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            <value>2003-05-14</value>
        </deemedExecutionDate>
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        </transactionTimeliness>
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    <nonDerivativeSecurity>
        <securityTitle>
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        </securityTitle>
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        <deemedExecutionDate>
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        </deemedExecutionDate>
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            <value></value>
        </transactionTimeliness>
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            </transactionShares>
            <transactionValue>
                <value>40.14</value>
            </transactionValue>
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            </transactionAcquiredDisposedCode>
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            <sharesOwnedFollowingTransaction>
                <value>67887.961</value>
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            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
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    </nonDerivativeSecurity>

    <nonDerivativeSecurity>
        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>
        <transactionDate>
            <value>2003-07-09</value>
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        <deemedExecutionDate>
            <value>2003-07-09</value>
        </deemedExecutionDate>
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            <transactionValue>
                <value>39.275</value>
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                <value>67904.944</value>
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            <directOrIndirectOwnership>
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    </nonDerivativeSecurity>

    <nonDerivativeSecurity>
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    <nonDerivativeSecurity>
        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>
        <transactionDate>
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        </transactionDate>
        <deemedExecutionDate>
            <value>2003-07-10</value>
        </deemedExecutionDate>
        <transactionCoding>
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            <transactionCode>S</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
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        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>4500</value>
            </transactionShares>
            <transactionValue>
                <value>39.076</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>D</value>
            </transactionAcquiredDisposedCode>
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        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>60904.944</value>
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        </ownershipNature>
    </nonDerivativeSecurity>

    <footnotes>
        <footnote id="F1">All Shares purchased in connection with Board of Directors adopted plan to invest earned Director fees in Company Common Stock.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Martin C. Ruegsegger as limited power of attorney for Donald S. Russell</signatureName>
        <signatureDate>2003-07-11</signatureDate>
    </ownerSignature>

</ownershipDocument>

