The photocatalytic decomposition of Probenazole in water using TiO2/H2O2 under sunlight illumination is studied. The addition of H2O2 is effective for the improvement of photocatalytic decomposition of Probenazole with TiO2. Furthermore, the operating conditions, such as photocatalyst dosage, temperature, pH, sunlight intensity and illumination time are also optimized. The kinetics of photocatalytic decomposition follow a pseudo-first-order kinetic law, and the rate constant is 0.129min(-1). The activation energy (E-a) is 11.34kJ/mol. The photocatalytic decomposition mechanism is discussed on the basis of molecular orbital (MO) simulation for frontier electron density.