The photocatalytic degradation of diuron in aqueous solution on TiO2 layer of a batch mode plate reactor irradiated with ultraviolet sun-bed tubes was investigated. Dependence of the reaction rate on the diuron concentration (in the range of 0.8-8.0 x 10(-5) mol dm(-3)) and on the light intensity (0.8-2.7 x 10(-9) einstein cm(-2) s(-1)) but independence on the flow rate (2.5-3.6 dm(3) min-(1)) were found. A reaction scheme was proposed following the main identified primary [3(3,4-dichlorophenyl)-1-methyl-1-formylurea and 3-(3,4-dichlorophenyl)-1-methylurea] and secondary [3-( 3,4-dichlorophenyl)-1-formylurea and 3,4-dichlorophenylurea] products.