<?xml version="1.0"?><ownershipDocument><schemaVersion>X0101</schemaVersion>    <documentType>4</documentType><periodOfReport>2003-07-23</periodOfReport><notSubjectToSection16>0</notSubjectToSection16><issuer><issuerCik>0000811669</issuerCik><issuerName>UST INC</issuerName>        <issuerTradingSymbol>UST</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId><rptOwnerCik>0001208563</rptOwnerCik><rptOwnerName>KESSLER MURRAY S</rptOwnerName></reportingOwnerId><reportingOwnerAddress><rptOwnerStreet1>  </rptOwnerStreet1><rptOwnerStreet2>  </rptOwnerStreet2><rptOwnerCity>  </rptOwnerCity><rptOwnerState>  </rptOwnerState><rptOwnerZipCode>  </rptOwnerZipCode></reportingOwnerAddress><reportingOwnerRelationship><isDirector>0</isDirector><isOfficer>1</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle>President (subsidiary)</officerTitle></reportingOwnerRelationship></reportingOwner><nonDerivativeSecurity><securityTitle><value>common stock</value></securityTitle><transactionDate><value>2003-07-23</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionTimeliness><value></value></transactionTimeliness><transactionAmounts><transactionShares><value>7800</value></transactionShares><transactionValue><value>0</value></transactionValue><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>26900</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership></ownershipNature></nonDerivativeSecurity><nonDerivativeSecurity><securityTitle><value>common stock</value></securityTitle><transactionDate><value>2003-07-24</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>M</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionTimeliness><value></value></transactionTimeliness><transactionAmounts><transactionShares><value>66700</value></transactionShares><transactionValue><value>15.06</value></transactionValue><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>93600</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership></ownershipNature></nonDerivativeSecurity><nonDerivativeSecurity><securityTitle><value>common stock</value></securityTitle><transactionDate><value>2003-07-24</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>S</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionTimeliness><value></value></transactionTimeliness><transactionAmounts><transactionShares><value>48200</value></transactionShares><transactionValue><value>33.32</value></transactionValue><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>46854</value><footnoteId id="F1" /></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership></ownershipNature></nonDerivativeSecurity><derivativeSecurity><securityTitle><value>Employee Stock Option (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>33.25</value></conversionOrExercisePrice><transactionDate><value>2003-07-23</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionTimeliness><value></value></transactionTimeliness><transactionAmounts><transactionShares><value>38900</value></transactionShares><transactionValue><value>33.25</value></transactionValue><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2004-07-23</value><footnoteId id="F2" /></exerciseDate><expirationDate><value>2013-07-22</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>common stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>38900</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>38900</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership></ownershipNature></derivativeSecurity><derivativeSecurity><securityTitle><value>Employee Stock Option (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>15.06</value></conversionOrExercisePrice><transactionDate><value>2003-07-24</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>M</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionTimeliness><value></value></transactionTimeliness><transactionAmounts><transactionShares><value>66700</value></transactionShares><transactionValue><value>15.06</value></transactionValue><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2002-07-10</value><footnoteId id="F3" /></exerciseDate><expirationDate><value>2010-07-09</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>common stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>66700</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>0</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership></ownershipNature></derivativeSecurity><footnotes><footnote id="F1">Includes a total of 1,454 shares held in the UST Inc. Employees' Savings Plan as of 6/30/2003.</footnote><footnote id="F2">Ratably over a three year period commencing on 7/23/2004.</footnote><footnote id="F3">33,300 shares became exercisable on 07/10/2002 and 33,400 shares became exercisable on 07/10/2003.</footnote></footnotes><ownerSignature><signatureName>Murray S. Kessler</signatureName><signatureDate>2003-07-24</signatureDate></ownerSignature></ownershipDocument>

