Using a mode-locked argon-ion laser and a time-correlated single-photon-counting detection system, the mechanism of supersensitization was explored with regard to the characteristics of light-induced electrons and holes in sensitizing dyes. In an optically excited supersensitized system, the fluorescence lifetime of a sensitizing dye adsorbed on AgBr microcrystals was shortened. Owing to hole trapping by a supersensitizer, electron transfer efficiency from a dye to AgBr microcrystals was found to be increase in the supersensitized systems examined.