Gold (Au) nanoparticles supported on cerium(IV) oxide (CeO2) were prepared by the photodeposition method. These samples showed strong absorption at around 550 nm due to localized surface plasmon resonance (LSPR) of Au. These Au/CeO2 samples were used for mineralization of organic acids (formic acid, oxalic acid and acetic acid) in the aqueous suspensions under irradiation of visible light (>ca. 520 nm) and three acids were stoichiometrically decomposed to carbon dioxide. Apparent activation energy for mineralization of formic acid was very small (2.4 kJ mol(-1)) compared with those by thermocatalytic reactions, and the action spectrum was in good agreement with the photoabsorption spectrum, indicating that the rate-determining step in mineralization of organic acids in the irradiated Au/CeO2 system was different from the thermal activation process and that this mineralization involved a photoinduced step by LSPR of Au supported on CeO2. When a green light-emitting diode (center wavelength = 530 nm) was used as the light source of visible light, mineralization of formic acid also occurred. Apparent quantum efficiency of formic acid mineralization increased with decrease in the intensity of the green light and reached 4.7% at 0.4 mW cm(-2). (C) 2011 Elsevier B.V. All rights reserved.