Photocatalytic degradation of the herbicide thiobencarb, monochlorobenzene and benzene was studied in aqueous TiO2 suspensions with a simulated sunlight, Pyrex-filtered xenon light (λ >290 nm). All these compounds were mineralized completely to carbon dioxide, and during the time-course of TOC, pH and anion were consistent. There were clear differences in the pH change and the time required for disappearance and mineralization between the three compounds.