Surface platinized TiO2 (Pt/TiO2) has been widely used and investigated but their properties are yet to be understood fully. Although it is known that the Pt effects depend on many experimental parameters and the kind of substrates, this study newly finds that the Pt effects could be also influenced by the light intensity. As for the photocatalytic degradation of trichloroethylene (TCE), the Pt effect was positive at high light intensity but was negative at low light intensity. A similar behavior was also observed in the photocurrent collection in the Pt/TiO2, suspension with polyoxometalate (POM: PW12O403-) used as an electron shuttle. The photocurrent collection in the Pt/TiO2 suspension was less efficient than in TiO2 suspension when the light intensity was low. Such abnormal light intensity-dependent behaviors were not observed in the photocatalytic degradation of dichloroacetate on Pt/TiO2 and the Fe3+-mediated photocurrent collection in the Pt/TiO2 suspension. It is proposed that the photochemical interactions between the Pt surface and reactive intermediates (TCE radical anions and reduced POM anions) induce a null reaction favorably at low light intensity condition. (c) 2005 Elsevier B.V. All rights reserved.