The photocatalysed degradation of two selected pesticide derivatives such as dichlorvos (1) and phosphamidon (2) has been investigated in aqueous suspensions of titanium dioxide. The degradation of 1 and 2 was monitored by the change in substrate concentration employing UV spectroscopic analysis as a function of irradiation time. The degradation kinetics was studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO2 and in the presence of electron acceptor such as hydrogen peroxide (H2O2) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other TiO2 powders. The pesticide derivative dichlorvos (1) was found to degrade faster as compared to phosphamidon (2). An attempt has also been made to identify the intermediate products of dichlorvos (1) formed during the photo-oxidation process through GC/MS analysis technique and probable pathway for the decomposition of dichlorovos (1) has been proposed.