Self-quenching of the triplet excited state of thiobenzophenone (TBP) was suppressed in a viscous alcoholic solution, an SDS micellar solution and an ionic liquid of TMPA TFSA. In those Solutions, the photochemical primary process of TBP could be studied by ns laser flash photolysis. Thiobenzophenone ketyl and phenylsulfanyl radicals were found to be generated from hydrogen abstraction of benzenethiol by TBP. The rate constant for the reaction was observed to be 1.1 x 10(7) s(-1) mol(-1) dm(3).