A simple, rapid, and highly selective spectrophotometric method for the simultaneous analysis of ozone (O-3) and hydrogen peroxide (H2O2) is proposed. On the basis of the large difference in the reaction rates of O-3 and H2O2 with I-, a changed absorbance corresponding to the reactions of the two species with I- was observed. This method enables a highly selective simultaneous analysis of O-3 and H2O2 in their coexistence.