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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-10-27</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001259388</rptOwnerCik>
            <rptOwnerName>ARMFIELD WILLIAM J IV</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>300 N GREENE ST SUITE 2190</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>GREENSBORO</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>27401</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>2010-10-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>10800</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>928315</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Stock Award of 10,800 shares under the 2008 Unifi, Inc. Long Term Incentive Plan.  Shares vest in three increments of 33 1/3%:  3,600 shares on 10/27/2011; 3,600 shares on 10/27/2012; and 3,600 shares on 10/27/2013.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/William J. Armfield, IV by Charles F. McCoy, POA</signatureName>
        <signatureDate>2010-10-28</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2010-10-27
0
0000100726
UNIFI INC
UFI
0001259388
ARMFIELD WILLIAM J IV
300 N GREENE ST SUITE 2190
GREENSBORO
NC
27401
1
0
0
0
Common Stock
2010-10-27
4
A
0
10800
0
A
928315
D
Stock Award of 10,800 shares under the 2008 Unifi, Inc. Long Term Incentive Plan.  Shares vest in three increments of 33 1/3%:  3,600 shares on 10/27/2011; 3,600 shares on 10/27/2012; and 3,600 shares on 10/27/2013.
/s/William J. Armfield, IV by Charles F. McCoy, POA
2010-10-28