The photocatalytic degradation of metoxuron [3-(3-chloro-4-methoxyphenyl)-1,1-dimethylurea] in aqueous suspensions of TiO2 was investigated. Several intermediate photoproducts were identified using NMR and MS techniques. Oxidation or removal of the methyl of terminal nitrogen and ring hydroxylation were found to occur. 2-Propanol was shown to decrease the rate of photocatalytic degradation, inhibiting partly ring hydroxylation and completely reactions on terminal nitrogen. In contrast, basification of the suspensions accelerated the degradation significantly. Degussa P25 TiO2 was found to exhibit a higher photocatalytic activity than Millennium TiO2 in spite of a generally smaller specific surface area. Within the Millennium TiO2 series, the photocatalytic efficiency increased with the specific surface area.