<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-03-12</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000100726</issuerCik>
        <issuerName>UNIFI INC</issuerName>
        <issuerTradingSymbol>UFI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001514905</rptOwnerCik>
            <rptOwnerName>Weinberger Mitchel</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>53 EAST 34TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PATERSON</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07514</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2014-03-12</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>25.21</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>35408</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>806511</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Dillon Yarn Corporation</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The Reporting Person is the President and Chief Operating Officer of Dillon Yarn Corporation, which owns 806,511 shares of the Registrant's common stock.  Pursuant to Instruction (4)(b)(iv) of Form 4, the Reporting Person disclaims beneficial ownership of any securities and any proceeds thereof that exceed his pecuniary interest therein and/or are not actually distributed to him.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/Mitchel Weinberger by W. Randy Eaddy, POA</signatureName>
        <signatureDate>2014-03-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2014-03-12
0
0000100726
UNIFI INC
UFI
0001514905
Weinberger Mitchel
53 EAST 34TH STREET
PATERSON
NJ
07514
1
0
0
0
COMMON STOCK
2014-03-12
4
S
0
2000
25.21
D
35408
D
COMMON STOCK
806511
I
by Dillon Yarn Corporation
The Reporting Person is the President and Chief Operating Officer of Dillon Yarn Corporation, which owns 806,511 shares of the Registrant's common stock.  Pursuant to Instruction (4)(b)(iv) of Form 4, the Reporting Person disclaims beneficial ownership of any securities and any proceeds thereof that exceed his pecuniary interest therein and/or are not actually distributed to him.
/s/Mitchel Weinberger by W. Randy Eaddy, POA
2014-03-13