Electro-oxidation of 3,4,3, 4-bis(ethylenedithio)-2,2,5,5-tetrathiafulvalen (abbr. ET) in the presence of allylsulfonate affords a new charge-transfer salt (ET)2(CH2=CH-CH2-SO3)H2O. The single crystal structure of the title compound is determined to be in orthorhombic crystal system, Pma2 space group. This salt is a semiconductor and its room-temperature conductivity is 0.0489Ω-1m-1.