-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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<SEC-DOCUMENT>0001501697-10-000001.txt : 20100924
<SEC-HEADER>0001501697-10-000001.hdr.sgml : 20100924
<ACCEPTANCE-DATETIME>20100924103535
ACCESSION NUMBER:		0001501697-10-000001
CONFORMED SUBMISSION TYPE:	D
PUBLIC DOCUMENT COUNT:		1
ITEM INFORMATION:		Rule 506
FILED AS OF DATE:		20100924
DATE AS OF CHANGE:		20100924
EFFECTIVENESS DATE:		20100924

FILER:

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Arsanis, Inc.
		CENTRAL INDEX KEY:			0001501697
		IRS NUMBER:				273181608
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		D
		SEC ACT:		1933 Act
		SEC FILE NUMBER:	021-148139
		FILM NUMBER:		101087999

	BUSINESS ADDRESS:	
		STREET 1:		16 CAVENDISH COURT
		CITY:			LEBANON
		STATE:			NH
		ZIP:			03766
		BUSINESS PHONE:		603-727-7107

	MAIL ADDRESS:	
		STREET 1:		16 CAVENDISH COURT
		CITY:			LEBANON
		STATE:			NH
		ZIP:			03766
</SEC-HEADER>
<DOCUMENT>
<TYPE>D
<SEQUENCE>1
<FILENAME>primary_doc.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<edgarSubmission>

    <schemaVersion>X0704</schemaVersion>

    <submissionType>D</submissionType>

    <testOrLive>LIVE</testOrLive>

    <primaryIssuer>
        <cik>0001501697</cik>
        <entityName>Arsanis, Inc.</entityName>
        <issuerAddress>
            <street1>16 CAVENDISH COURT</street1>
            <city>LEBANON</city>
            <stateOrCountry>NH</stateOrCountry>
            <stateOrCountryDescription>NEW HAMPSHIRE</stateOrCountryDescription>
            <zipCode>03766</zipCode>
        </issuerAddress>
        <issuerPhoneNumber>603-727-7107</issuerPhoneNumber>
        <jurisdictionOfInc>DELAWARE</jurisdictionOfInc>
        <issuerPreviousNameList>
            <value>None</value>
        </issuerPreviousNameList>
        <edgarPreviousNameList>
            <value>None</value>
        </edgarPreviousNameList>
        <entityType>Corporation</entityType>
        <yearOfInc>
            <withinFiveYears>true</withinFiveYears>
            <value>2010</value>
        </yearOfInc>
    </primaryIssuer>

    <relatedPersonsList>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Tillman</firstName>
                <middleName>U.</middleName>
                <lastName>Gerngross</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>16 Cavendish Court</street1>
                <city>Lebanon</city>
                <stateOrCountry>NH</stateOrCountry>
                <stateOrCountryDescription>NEW HAMPSHIRE</stateOrCountryDescription>
                <zipCode>03766</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Errik</firstName>
                <middleName>B.</middleName>
                <lastName>Anderson</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>16 Cavendish Court</street1>
                <city>Lebanon</city>
                <stateOrCountry>NH</stateOrCountry>
                <stateOrCountryDescription>NEW HAMPSHIRE</stateOrCountryDescription>
                <zipCode>03766</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Robert</firstName>
                <middleName>L.</middleName>
                <lastName>Birnbaum</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>c/o Foley Hoag LLP</street1>
                <street2>155 Seaport Boulevard</street2>
                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
                <zipCode>02210</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Executive Officer</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Terrance</firstName>
                <lastName>McGuire</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>c/o Polaris Venture Partners</street1>
                <street2>1000 Winter Street, Suite 3350</street2>
                <city>Waltham</city>
                <stateOrCountry>MA</stateOrCountry>
                <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
                <zipCode>02451</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Michael</firstName>
                <lastName>Ross</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>c/o SV Life Sciences</street1>
                <street2>60 State Street, Suite 3650</street2>
                <city>Boston</city>
                <stateOrCountry>MA</stateOrCountry>
                <stateOrCountryDescription>MASSACHUSETTS</stateOrCountryDescription>
                <zipCode>02109</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
        <relatedPersonInfo>
            <relatedPersonName>
                <firstName>Carl</firstName>
                <lastName>Gordon</lastName>
            </relatedPersonName>
            <relatedPersonAddress>
                <street1>c/o Caduceus Private Investments</street1>
                <street2>767 Third Avenue, 30th Floor</street2>
                <city>New York</city>
                <stateOrCountry>NY</stateOrCountry>
                <stateOrCountryDescription>NEW YORK</stateOrCountryDescription>
                <zipCode>10017</zipCode>
            </relatedPersonAddress>
            <relatedPersonRelationshipList>
                <relationship>Director</relationship>
            </relatedPersonRelationshipList>
            <relationshipClarification></relationshipClarification>
        </relatedPersonInfo>
    </relatedPersonsList>

    <offeringData>
        <industryGroup>
            <industryGroupType>Biotechnology</industryGroupType>
        </industryGroup>
        <issuerSize>
            <revenueRange>Decline to Disclose</revenueRange>
        </issuerSize>
        <federalExemptionsExclusions>
            <item>06</item>
        </federalExemptionsExclusions>
        <typeOfFiling>
            <newOrAmendment>
                <isAmendment>false</isAmendment>
            </newOrAmendment>
            <dateOfFirstSale>
                <value>2010-09-15</value>
            </dateOfFirstSale>
        </typeOfFiling>
        <durationOfOffering>
            <moreThanOneYear>false</moreThanOneYear>
        </durationOfOffering>
        <typesOfSecuritiesOffered>
            <isEquityType>true</isEquityType>
        </typesOfSecuritiesOffered>
        <businessCombinationTransaction>
            <isBusinessCombinationTransaction>false</isBusinessCombinationTransaction>
            <clarificationOfResponse></clarificationOfResponse>
        </businessCombinationTransaction>
        <minimumInvestmentAccepted>882</minimumInvestmentAccepted>
        <salesCompensationList></salesCompensationList>
        <offeringSalesAmounts>
            <totalOfferingAmount>400002</totalOfferingAmount>
            <totalAmountSold>400002</totalAmountSold>
            <totalRemaining>0</totalRemaining>
            <clarificationOfResponse></clarificationOfResponse>
        </offeringSalesAmounts>
        <investors>
            <hasNonAccreditedInvestors>false</hasNonAccreditedInvestors>
            <totalNumberAlreadyInvested>7</totalNumberAlreadyInvested>
        </investors>
        <salesCommissionsFindersFees>
            <salesCommissions>
                <dollarAmount>0</dollarAmount>
            </salesCommissions>
            <findersFees>
                <dollarAmount>0</dollarAmount>
            </findersFees>
            <clarificationOfResponse></clarificationOfResponse>
        </salesCommissionsFindersFees>
        <useOfProceeds>
            <grossProceedsUsed>
                <dollarAmount>0</dollarAmount>
            </grossProceedsUsed>
            <clarificationOfResponse></clarificationOfResponse>
        </useOfProceeds>
        <signatureBlock>
            <authorizedRepresentative>false</authorizedRepresentative>
            <signature>
                <issuerName>Arsanis, Inc.</issuerName>
                <signatureName>Robert L. Birnbaum</signatureName>
                <nameOfSigner>Robert L. Birnbaum</nameOfSigner>
                <signatureTitle>Secretary</signatureTitle>
                <signatureDate>2010-09-23</signatureDate>
            </signature>
        </signatureBlock>
    </offeringData>
</edgarSubmission>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----