Abstract: The feasibility of photocatalytic degradation of monocrotophos pesticides using thin film of TiO₂ was studied. The results showed that 0.65×10^-4 mol/L of monocrotophos can be completely photocatalytically degraded into PO₄^3- after 60min illumination with a medium pressure mercury lamp of 375 W, the photodegradation efficiency was raised respectively by adding a little amount of H₂O₂or Fe³⁺+. The effects of amount of TiO₂, initial pH and flow rate of air on the photocatalytic degradation of monocrotophos were also investigated. After 80 h illumination no significant loss of photocatalytic activity of TiO₂ was found.