A chemiluminescent probe, luminol, was successfully applied to monitoring superoxide ions (O-2 radical anion) and hydrogen peroxide (H2O2) produced on photocatalytic reaction in aqueous TiO2 suspension. Two chemiluminescent reactions were distinguished from the decay profile after the end of the irradiation, and the reaction mechanism was analyzed. The fast decay component gives information about O-2 radical anion and the slow one provides the amount of H2O2. The pale constant for the reaction of O-2 radical anion with luminol was found to be 1 x 10(4) M-1 s(-1). The amount of O-2 radical anion during the irradiation on TiO2 in alkaline solution could be estimated to be on the order of 10(-13) M. Detection of H2O2 in concentrations as small as 10(-9) M was demonstrated in the photocatalytic water oxidation.