The decomposition of fenuron (1,1-dimethyl-3-phenylurea), a herbicide regarded as a priority pollutant, was carried out in batch reactors by means of ozone, UV radiation,,and Fenton's' reagent as single oxidants and by the advanced oxidation processes formed, by the following combinations: UV radiation plus H2O2, U-V radiation plus Fenton's reagent (photo-Fenton system), ozone plus UV radiation, and ozone plus U-V radiation and H2O2. In all cases, the decomposition levels were determined and the apparent pseudo-first-order..,,rate constants were evaluated by linear regression to compare the efficiencies of the processes: The, rate constants for the reactions of fenuron with ozone and with hydroxyl, radicals were determined as well as the efficiencies for the photodecomposition by direct UV radiation. Finally, in the combined systems, the contributions to the overall decomposition caused by the radical reactions were established by calculating the radical rate constants.