This paper studies the feasibility of photocatalytic degradation of organophosphorus pesticides using thin films of TiO2. The results show that 0.65 x 10(-4) mol dm(-3) of dichlorvos, monocrotophos, phorate, parathion can be completely photocatalytically degraded into PO43- within a short time under illumination with a medium pressure mercury lamp of 375 W. The effects of parameters such as the amount of TiO2 attached, initial concentration of organophosphorus pesticides, initial pH, amount of air how, concentrations of H2O2 and Fe3+ on the photocatalytic degradation are studied. The possible mechanisms of photocatalytic degradation are discussed. It is our assumption that the degradation reactions occur on the surface of TiO2 via primary produced oxidizing species such as the OH radical and O-2(2-.). After 80 h illumination, there is no significant loss of the photocatalytic activity of TiO2.