The photocatalytic degradation of a commercial azo dye Benzopurpurine 4B (BP4B) in aqueous solution was investigated under UV-A light at different operating conditions, including irradiation time, pH solution, initial dye concentration, amount of catalyst, light intensity as well as band gap of other semiconductor groups by UV-spectrophotometric monitoring. The highest decomposition efficiency was obtained at pH 8 as a result of 97.24 % degradation of BP4B for 80 min of irradiation time. Photodecomposition reaction of BP4B dye was correlated with pseudo-first-order kinetic model. The degradation data of BP4B dye were satisfactory described by Langmuir-Hinshelwood (L-H) mechanism.