    <SEC-DOCUMENT>0001485003-22-000031-index.html : 20220228
    <SEC-HEADER>0001485003-22-000031.hdr.sgml : 20220228
    <ACCEPTANCE-DATETIME>20220228081513
    ACCESSION NUMBER:		0001485003-22-000031
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		21
    CONFORMED PERIOD OF REPORT:	20220228
    ITEM INFORMATION:		Results of Operations and Financial Condition
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20220228
    DATE AS OF CHANGE:		20220228

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			Sesen Bio, Inc.
    		CENTRAL INDEX KEY:			0001485003
    		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
    		IRS NUMBER:				262025616
    		STATE OF INCORPORATION:			DE
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		8-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	001-36296
    		FILM NUMBER:		22684008

    	BUSINESS ADDRESS:
    		STREET 1:		245 FIRST STREET
    		STREET 2:		SUITE 1800
    		CITY:			CAMBRIDGE
    		STATE:			MA
    		ZIP:			02142
    		BUSINESS PHONE:		617-444-8550

    	MAIL ADDRESS:
    		STREET 1:		245 FIRST STREET
    		STREET 2:		SUITE 1800
    		CITY:			CAMBRIDGE
    		STATE:			MA
    		ZIP:			02142

    	FORMER COMPANY:
    		FORMER CONFORMED NAME:	Eleven Biotherapeutics, Inc.
    		DATE OF NAME CHANGE:	20100223
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>8-K
    <SEQUENCE>1
    <FILENAME>sesn-20220228.htm
    <DESCRIPTION>8-K
    <TEXT>
    Document 1 - file: sesn-20220228.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-99.1
    <SEQUENCE>2
    <FILENAME>a4q2021earningspressrele.htm
    <DESCRIPTION>EX-99.1
    <TEXT>
    Document 2 - file: a4q2021earningspressrele.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-101.SCH
    <SEQUENCE>3
    <FILENAME>sesn-20220228.xsd
    <DESCRIPTION>XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT
    <TEXT>
    Document 3 - file: sesn-20220228.xsd

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-101.LAB
    <SEQUENCE>4
    <FILENAME>sesn-20220228_lab.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION LABEL LINKBASE DOCUMENT
    <TEXT>
    Document 4 - file: sesn-20220228_lab.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-101.PRE
    <SEQUENCE>5
    <FILENAME>sesn-20220228_pre.xml
    <DESCRIPTION>XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE DOCUMENT
    <TEXT>
    Document 5 - file: sesn-20220228_pre.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>6
    <FILENAME>a4q2021earningspressrele001.jpg
    <TEXT>
    Document 6 - file: a4q2021earningspressrele001.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>7
    <FILENAME>a4q2021earningspressrele002.jpg
    <TEXT>
    Document 7 - file: a4q2021earningspressrele002.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>8
    <FILENAME>a4q2021earningspressrele003.jpg
    <TEXT>
    Document 8 - file: a4q2021earningspressrele003.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>9
    <FILENAME>a4q2021earningspressrele004.jpg
    <TEXT>
    Document 9 - file: a4q2021earningspressrele004.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>10
    <FILENAME>a4q2021earningspressrele005.jpg
    <TEXT>
    Document 10 - file: a4q2021earningspressrele005.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>11
    <FILENAME>a4q2021earningspressrele006.jpg
    <TEXT>
    Document 11 - file: a4q2021earningspressrele006.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>12
    <FILENAME>a4q2021earningspressrele007.jpg
    <TEXT>
    Document 12 - file: a4q2021earningspressrele007.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>13
    <FILENAME>a4q2021earningspressrele008.jpg
    <TEXT>
    Document 13 - file: a4q2021earningspressrele008.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>14
    <FILENAME>R1.htm
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 14 - file: R1.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>15
    <FILENAME>sesn-20220228_htm.xml
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 15 - file: sesn-20220228_htm.html

    Document 15 - RAW XML: sesn-20220228_htm.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EXCEL
    <SEQUENCE>16
    <FILENAME>Financial_Report.xlsx
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 16 - file: Financial_Report.xlsx

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>17
    <FILENAME>Show.js
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 17 - file: Show.js

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>18
    <FILENAME>report.css
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 18 - file: report.css

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>19
    <FILENAME>FilingSummary.xml
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 19 - file: FilingSummary.html

    Document 19 - RAW XML: FilingSummary.xml

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>JSON
    <SEQUENCE>21
    <FILENAME>MetaLinks.json
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 21 - file: MetaLinks.json

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>ZIP
    <SEQUENCE>22
    <FILENAME>0001485003-22-000031-xbrl.zip
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
    Document 22 - file: 0001485003-22-000031-xbrl.zip

    </DOCUMENT>
    </SEC-DOCUMENT>