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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-05-12</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

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            <rptOwnerName>COX ARCHIBALD JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O UNIFI, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>7201 W. FRIENDLY AVENUE</rptOwnerStreet2>
            <rptOwnerCity>GREENSBORO</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>27410</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

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                <value>COMMON STOCK</value>
            </securityTitle>
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            </transactionDate>
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                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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                <value></value>
            </transactionTimeliness>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
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                </directOrIndirectOwnership>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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        <nonDerivativeTransaction>
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            <transactionDate>
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                <transactionCode>S</transactionCode>
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            <transactionTimeliness>
                <value></value>
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                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
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                </sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
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        <nonDerivativeTransaction>
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                <transactionCode>S</transactionCode>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
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                <transactionShares>
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                <transactionPricePerShare>
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                </transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
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                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
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        <nonDerivativeTransaction>
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                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
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            </transactionDate>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4100</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
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        <nonDerivativeTransaction>
            <securityTitle>
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            <transactionDate>
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                <transactionCode>S</transactionCode>
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            <transactionTimeliness>
                <value></value>
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            <transactionAmounts>
                <transactionShares>
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                <transactionPricePerShare>
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                <transactionPricePerShare>
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    </nonDerivativeTable>

    <ownerSignature>
        <signatureName>/S/Archibald Cox, Jr./Charles F. McCoy, POA</signatureName>
        <signatureDate>2010-05-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2010-05-12
0
0000100726
UNIFI INC
UFI
0001020707
COX ARCHIBALD JR
C/O UNIFI, INC.
7201 W. FRIENDLY AVENUE
GREENSBORO
NC
27410
1
0
0
0
COMMON STOCK
2010-05-12
4
S
0
81900
4.05
D
643100
D
COMMON STOCK
2010-05-12
4
S
0
10500
4.06
D
632600
D
COMMON STOCK
2010-05-12
4
S
0
11200
4.07
D
621400
D
COMMON STOCK
2010-05-12
4
S
0
10700
4.08
D
610700
D
COMMON STOCK
2010-05-12
4
S
0
12500
4.09
D
598200
D
COMMON STOCK
2010-05-12
4
S
0
8900
4.1
D
589300
D
COMMON STOCK
2010-05-12
4
S
0
4100
4.11
D
585200
D
COMMON STOCK
2010-05-12
4
S
0
100
4.1186
D
585100
D
COMMON STOCK
2010-05-12
4
S
0
9200
4.12
D
575900
D
COMMON STOCK
2010-05-12
4
S
0
200
4.1243
D
575700
D
COMMON STOCK
2010-05-12
4
S
0
15300
4.13
D
560400
D
COMMON STOCK
2010-05-12
4
S
0
1800
4.14
D
558600
D
COMMON STOCK
2010-05-12
4
S
0
200
4.15
D
558400
D
/S/Archibald Cox, Jr./Charles F. McCoy, POA
2010-05-13