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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-10-22</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001131033</rptOwnerCik>
            <rptOwnerName>PERKINS GEORGE R JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>306 MCINTOSH STREET, SUITE B</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SANFORD</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>27330</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Former Director</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-10-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3333</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>8.16</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>353873</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>8.16</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2014-10-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3333</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-10-24</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3333</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">An adjustment was made reducing the total number of directly owned shares held by the Reporting Person by 1 share as the amount of shares gifted on 6/18/2014 was incorrectly stated as being 1,866 instead of 1,867 shares.</footnote>
        <footnote id="F2">The Options vested and became exercisable on the date that the closing price of the Registrant's common stock on the New York Stock Exchange was at least $24.00 per share for thirty (30) consecutive trading days.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/George R. Perkins, Jr. by W. Randy Eaddy, POA</signatureName>
        <signatureDate>2014-10-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2014-10-22
1
0000100726
UNIFI INC
UFI
0001131033
PERKINS GEORGE R JR
306 MCINTOSH STREET, SUITE B
SANFORD
NC
27330
0
0
0
1
Former Director
Common Stock
2014-10-22
4
M
0
3333
8.16
A
353873
D
Stock Option (Right to Buy)
8.16
2014-10-22
4
M
0
3333
0
D
2017-10-24
Common Stock
3333
0
D
An adjustment was made reducing the total number of directly owned shares held by the Reporting Person by 1 share as the amount of shares gifted on 6/18/2014 was incorrectly stated as being 1,866 instead of 1,867 shares.
The Options vested and became exercisable on the date that the closing price of the Registrant's common stock on the New York Stock Exchange was at least $24.00 per share for thirty (30) consecutive trading days.
/s/George R. Perkins, Jr. by W. Randy Eaddy, POA
2014-10-24