Au particles (mean size ca. 3 nm) supported on TiO2 particles were irradiated by UV light (> 300 nm) in aqueous solutions at 278 K. Photoinduced dissolution of Au nanoparticles followed by redeposition occurred in aqueous solutions containing halogen ions. The dissolution of An nanoparticles yielded a Au(III) complex with a halogen ion; subsequent reduction of the Au(III) complex caused precipitation of larger An particles on TiO2,. (c) 2005 Elsevier Inc. All rights reserved.