The photocatalyzed degradation of a pesticide derivative, 3-chloro-4-methoxyaniline (1), has been investigated in aqueous suspensions of titanium dioxide (TiO2) and air as a function of irradiation time under a variety of conditions using UV-Vis spectroscopic and HPLC analysis techniques. The degradation kinetics were studied under different conditions such as types of TiO2 powders, reaction pH, catalyst loading, substrate, and H2O2 concentrations. The photocatalyst Degussa P25 showed better photocatalytic activity for the degradation of the compound 1. Addition of hydrogen peroxide as an electron acceptor in addition to oxygen greatly enhanced the degradation rate of the compound 1. Higher degradation rates were observed at lower and higher pH values, i.e., 3.15 and 9.15, respectively. The optimal substrate concentration and catalyst loading for the degradation was found to be 0.6 mM with 1.5 g L-1. A probable pathway for the decomposition of compound 1 is proposed.