Supported titanium dioxide (TiO2) was investigated for the photodegradation of the insecticide fenamiphos in water. The photocatalyst was immobilised on borosilicate glass plates and the kinetics of degradation were studied in a stirred tank reactor under UV irradiation. Two types of TiO2, for example, Millennium PC500 (100% anatase) and Degussa P25 (80% anatase, 20%rutile), were used. Their activities have been based on the rates of insecticide disappearance. Experiments were investigated to evaluate the effect of pH and initial concentrations of fenamiphos as well as catalyst doses on the photocatalytic degradation of fenamiphos. Kinetic parameters were experimentally determined and an apparent first-order kinetic was observed. For photolysisprocess of fenamiphos, two photoproducts were identified and characterized using high performance liquid chromatography/mass spectrometry (HPLC/MS). The plausible mechanism of photolysis involved is the oxidation of sulfonamide group. In presence of photocatalyst TiO2, photodegradation was observed. Under identical conditions, Degussa P25 shows higher photocatalytic activity in regard to PC500 Millennium and complete degradation was observed after 180 min.