Benzophenone-3 (BP-3), an organic ultraviolet (UV) filter, is reported to exhibit endocrine disruptive effects. In this study, the degradation of BP-3 by UV/H2O2 in aqueous solution was investigated by steady-state photolysis and laser flash photolysis experiments. The photolysis of BP-3 was not observed obviously after 8 h under UV irradiation (λ = 254 nm), but the degradation of BP-3 could be conducted via UV/H2O2 due to the oxidation by hydroxyl radical (HOradical dot). At higher initial concentrations of BP-3, the degradation percentages decreased, and the optimal pH for the degradation of BP-3 was 6.0. The reaction of BP-3 and HOradical dot adhered to the pseudo-first-order kinetics. When the BP-3 concentration was 0.01 mM, the rate constants of the apparent first-order reaction and second-order reaction between BP-3 and HOradical dot were 1.26 × 10−3 s−1 and 2.97 × 1010 M−1 s−1, respectively. Several intermediate products were obtained and the primary reaction pathway of BP-3 and HOradical dot was proposed.