The photocatalytic degradation of technical grade pesticide 'malathion' has been studied in aqueous suspensions of TiO2. The main aim of using this process is to degrade the toxic complex structure of the pesticide to harmless products by treating the sample in the UV-reactor. The COD measurements are carried out in order to study the percentage mineralization and degradation is studied under different parameters like varying pH, catalyst concentration, and oxidant addition (H2O2). The degradation of the pesticide is found to be maximum at optimum catalyst loading of 3.0 g/L, pH of 6.0 and oxidant concentration of 2.5 mL/200 mL. Adsorption is negligible as compared to photocatalytic degradation of the pesticide.