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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-06-21</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001344413</issuerCik>
        <issuerName>Alexza Pharmaceuticals Inc.</issuerName>
        <issuerTradingSymbol>ALXA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001316623</rptOwnerCik>
            <rptOwnerName>Read J Leighton</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ALEXZA PHARMACEUTICALS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2091 STIERLIN COURT</rptOwnerStreet2>
            <rptOwnerCity>MOUNTAIN VIEW</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94043</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>
            <transactionDate>
                <value>2016-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
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                <transactionFormType>4</transactionFormType>
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                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
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            </securityTitle>
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            <transactionDate>
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            <deemedExecutionDate></deemedExecutionDate>
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            <transactionTimeliness>
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            <exerciseDate>
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            <expirationDate>
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                </underlyingSecurityTitle>
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            </underlyingSecurity>
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        <derivativeTransaction>
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            <transactionDate>
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            <deemedExecutionDate></deemedExecutionDate>
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            <exerciseDate>
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            <expirationDate>
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            <underlyingSecurity>
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                </underlyingSecurityTitle>
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                </underlyingSecurityShares>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
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            <transactionDate>
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            <deemedExecutionDate></deemedExecutionDate>
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            <transactionTimeliness>
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            <transactionAmounts>
                <transactionShares>
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                    <footnoteId id="F2"/>
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                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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            <exerciseDate>
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            </exerciseDate>
            <expirationDate>
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            </expirationDate>
            <underlyingSecurity>
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                <underlyingSecurityShares>
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            </underlyingSecurity>
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                </sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
                    <value>D</value>
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            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>3.50</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3991</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2012-07-06</value>
            </exerciseDate>
            <expirationDate>
                <value>2022-06-06</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
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                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3991</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>15.30</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3125</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2011-08-28</value>
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            <expirationDate>
                <value>2021-07-28</value>
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            <underlyingSecurity>
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            </underlyingSecurity>
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                <directOrIndirectOwnership>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>35.20</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
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                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
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            <transactionAmounts>
                <transactionShares>
                    <value>625</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2010-06-18</value>
            </exerciseDate>
            <expirationDate>
                <value>2020-05-18</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
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                </underlyingSecurityShares>
            </underlyingSecurity>
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                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>16.90</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
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            <transactionTimeliness>
                <value></value>
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            <transactionAmounts>
                <transactionShares>
                    <value>625</value>
                    <footnoteId id="F2"/>
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                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2009-06-07</value>
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            <expirationDate>
                <value>2019-05-07</value>
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                <underlyingSecurityTitle>
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        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
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            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-06-21</value>
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            <deemedExecutionDate></deemedExecutionDate>
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                <value></value>
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            <transactionAmounts>
                <transactionShares>
                    <value>625</value>
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                <transactionPricePerShare>
                    <value>0.00</value>
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                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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            <exerciseDate>
                <value>2008-06-27</value>
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            <expirationDate>
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                <sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>98.50</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
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                <transactionFormType>4</transactionFormType>
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            <transactionTimeliness>
                <value></value>
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            <transactionAmounts>
                <transactionShares>
                    <value>625</value>
                    <footnoteId id="F2"/>
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                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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            <exerciseDate>
                <value>2007-06-23</value>
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            <expirationDate>
                <value>2017-05-23</value>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
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                </underlyingSecurityShares>
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                <sharesOwnedFollowingTransaction>
                    <value>0</value>
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        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Per the terms of the Agreement and Plan of Merger, dated 5/9/16, among the Issuer, Grupo Ferrer Internactional, S.A. and Ferrer Pharma Inc. (the &quot;Agreement) and the Offer (as defined in the Agreement), each share of the Issuer's common stock was tendered for $0.90 per share in cash, without interest and less any required withholding taxes, plus one contractual contingent value right per share (&quot;CVR&quot;) (as defined in the Agreement).</footnote>
        <footnote id="F2">Disposed of per Section 3.4(a) of the Agreement, whereby each option that was outstanding immediately prior to the Offer Closing (as defined in the Agreement) was cancelled without consideration.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Brent D. Fassett, as Attorney-in-Fact for J. Leighton Read</signatureName>
        <signatureDate>2016-06-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
