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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2015-09-28</periodOfReport>

    <dateOfOriginalSubmission>2015-09-28</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001623398</rptOwnerCik>
            <rptOwnerName>Grupo Ferrer Internacional, S.A.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>AVENIDA DIAGONAL 549</rptOwnerStreet1>
            <rptOwnerStreet2>5TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>BARCELONA</rptOwnerCity>
            <rptOwnerState>U3</rptOwnerState>
            <rptOwnerZipCode>E-08029</rptOwnerZipCode>
            <rptOwnerStateDescription>SPAIN</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001668295</rptOwnerCik>
            <rptOwnerName>Ferrer-Salat Sergio</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>AVENIDA DIAGONAL 549</rptOwnerStreet1>
            <rptOwnerStreet2>5TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>BARCELONA</rptOwnerCity>
            <rptOwnerState>U3</rptOwnerState>
            <rptOwnerZipCode>E-08029</rptOwnerZipCode>
            <rptOwnerStateDescription>SPAIN</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-09-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>125000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2366935</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The shares were issued as partial consideration for a term loan in the maximum principal amount of $5 million with an interest rate of 6% per annum from the Reporting Person to the Issuer as reported in Current Report on Form 8-K on the date hereof.</footnote>
        <footnote id="F2">Mr. Ferrer-Salat, as the Chairman and controlling shareholder of Grupo Ferrer Internacional S.A. (&quot;Grupo Ferrer&quot;) may be deemed a beneficial owner of the securities held by Grupo Ferrer, but disclaims ownership thereof except to the extent of his pecuniary interest therein.</footnote>
    </footnotes>

    <remarks>This Form 4/A amends a Form 4 filed on September 28, 2015 and is being filed in order to add Sergio Ferrer-Salat as a reporting person.</remarks>

    <ownerSignature>
        <signatureName>Grupo Ferrer Internacional, S.A., By: /s/ Jorge Ramentol Massana, C.E.O and By: /s/ Juan Fanes Trillo, C.F.O.</signatureName>
        <signatureDate>2016-03-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Sergio Ferrer-Salat</signatureName>
        <signatureDate>2016-03-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
