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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-04-30</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001491847</rptOwnerCik>
            <rptOwnerName>Oki Mark K</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ALEXZA PHARMACEUTICALS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2091 STIERLIN COURT</rptOwnerStreet2>
            <rptOwnerCity>MOUNTAIN VIEW</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94043</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, CFO &amp; Secretary</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>55463</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Includes 2,000 shares acquired under the Alexza Pharmaceuticals, Inc. 2005 Employee Stock Purchase Plan on April 30, 2014.</footnote>
        <footnote id="F2">Includes 43,750 previously reported shares issued as restricted stock units (&quot;RSUs&quot;) under the Issuer's 2005 Equity Incentive Plan (the &quot;Plan&quot;). If the Issuer's common stock listed on the Nasdaq Global Market has traded at or above $8.63 on each trading day of any 30-day trading period after March 29, 2013 (the &quot;Price Trigger&quot;), then 50% of the RSUs will vest on the later of March 29, 2016 and the date on which the Price Trigger is met, and the remaining 50% of the RSUs will vest on the later of March 29, 2017 and the date on which the Price Trigger is met, provided in each case that the Reporting Person remains employed by the Company through the applicable vesting date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Brent D. Fassett, Attorney-in-Fact</signatureName>
        <signatureDate>2014-05-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
