The photocatalytic degradation of fenitrothion under UV and near visible light in the presence of polyoxometallate (POM) photocatalyst PW12O403-, in aqueous solutions has been studied and compared with the photodegradation by TiO2 suspensions. Fenitrothion is effectively degraded in the presence of both photocatalysts following pseudo first order kinetics. Complete mineralization of fenitrothion is achieved using both photocatalysts, leading to the formation Of CO2 and inorganic ions (PO43-, SO42-, NO2-, and NO3-) as final products. Various inermediates, identical in the presence of both photocatalysts, have been detected and identified using HPLC and GC-MS techniques. The similarity of the intermediates by these two methods, i.e. PW12O403-and TiO2 tends to suggest, that the photodegradation mechanism of fenitrothion as other cases as well, takes place mainly via a common reagent, i.e. OH radicals. A photodegradation mechanism is proposed. Photolysis of fenitrothion, i.e. in the absence of catalysts is very slow and far from producing complete mineralization. A relatively large number of intermediates is observed, most of which are not detected in the photocatalytic processes. (C) 2003 Elsevier B.V. All rights reserved.