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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-01-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000726517</issuerCik>
        <issuerName>MERCHANTS BANCSHARES INC</issuerName>
        <issuerTradingSymbol>mbvt</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001220456</rptOwnerCik>
            <rptOwnerName>TUTTLE MICHAEL R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>275 KENNEDY DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SOUTH BURLINGTON</rptOwnerCity>
            <rptOwnerState>VT</rptOwnerState>
            <rptOwnerZipCode>05403</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-01-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>15150</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>18.5</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>40559.22</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-01-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>12196</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.96</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>29363.22</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7474.74</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By 401(k)</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>August 1997 Option Grant</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>18.5</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-01-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>15150</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>18.5</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>1999-08-28</value>
            </exerciseDate>
            <expirationDate>
                <value>2007-08-28</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>15150</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeHolding>
            <securityTitle>
                <value>August 1998 Option Grant</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>20.33</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2000-08-20</value>
            </exerciseDate>
            <expirationDate>
                <value>2008-08-20</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>13278</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13278</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>August 1999 Option Grant</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>17.5</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2001-08-19</value>
            </exerciseDate>
            <expirationDate>
                <value>2009-08-19</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>14495</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14495</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The reporting person's beneficial holdings of Company stock includes dividend reinvestment plan, which provides for the regular reinvestment of dividends, broad-based participation and operates on substantially the same terms for all plan particpants.</footnote>
        <footnote id="F2">The reporting person's indirect holdings of Company stock includes shares acquired through the Company's 401(k) plan, which provides for regular employee payroll contributions to the plan, regular reinvestment of dividends, broad-based participation, and operates on substntially the same terms for all plan participants.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Lisa A. Razo, P.O.A. for Michael R. Tuttle</signatureName>
        <signatureDate>2007-02-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-01-31
0
0000726517
MERCHANTS BANCSHARES INC
mbvt
0001220456
TUTTLE MICHAEL R
275 KENNEDY DRIVE
SOUTH BURLINGTON
VT
05403
1
1
0
0
President and CEO
Common Stock
2007-01-31
4
M
0
15150
18.5
A
40559.22
D
Common Stock
2007-01-31
4
F
0
12196
22.96
D
29363.22
D
Common Stock
7474.74
I
By 401(k)
August 1997 Option Grant
18.5
2007-01-31
4
M
0
15150
18.5
D
1999-08-28
2007-08-28
Common Stock
15150
0
D
August 1998 Option Grant
20.33
2000-08-20
2008-08-20
Common Stock
13278
13278
D
August 1999 Option Grant
17.5
2001-08-19
2009-08-19
Common Stock
14495
14495
D
The reporting person's beneficial holdings of Company stock includes dividend reinvestment plan, which provides for the regular reinvestment of dividends, broad-based participation and operates on substantially the same terms for all plan particpants.
The reporting person's indirect holdings of Company stock includes shares acquired through the Company's 401(k) plan, which provides for regular employee payroll contributions to the plan, regular reinvestment of dividends, broad-based participation, and operates on substntially the same terms for all plan participants.
Lisa A. Razo, P.O.A. for Michael R. Tuttle
2007-02-01