The decolouring and the degradation of xylenot orange in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized palladium particles has been studied. The photocatalytic activity of TiO2, modified with palladium, is higher than that of the semiconductig support. The adsorption properties of the catalysts, as well as the size of the palladium clusters on the surface of the support, influence the efficiency of the photocatalytic process. The rate of disappearance of the dye molecule follows a pseudo-first kinetic order according to the Langmuir-Hinshelwood model. The increase of the quantum yield of the photodestruction reaction of the studied dye is due to the formation of Schotky barriers on the metal-semiconductor interface, which serve as efficient electron traps, preventing the electron-hole recombination. (C) 2004 Elsevier B.V. All rights reserved.