Cerium dioxide was prepared by the precipitation method and found to be an efficient photocatalyst to degrade azodyes under visible light irradiation. Nonbiodegradable azodyes acid orange 7 (AO7) was selected as modal target to examine the photocatalytic activity of CeO2. AO7 could be efficiently degraded in aqueous suspension of CeO2 under visible light illumination. The catalyst was characterized by X-ray diffraction (XRD), N-2 sorption, transmission electron microscopic image (TEM) and UV/vis absorption spectrum techniques. AO7 solution was quickly decolorized and partly mineralized under visible light irradiation with existing CeO2. The photodegradation rate of this azodye catalyzed by CeO2 is much faster than those occurring on commercial titania (Degussa P25) under otherwise identical conditions of visible light irradiation. Experiments were conducted to examine the adsorption mode of acid orange 7 on CeO2 and adsorption capacity at different pH values. The possible degradation pathway has been proposed for the photocatalytic degradations by using certain radical scavengers and gas chromatography-mass spectrometry (GC-MS) to determine intermediates. The enhanced photoactivity of the lanthanide oxide CeO2 was attributed to the superior adsorption capacity and special 4f electron configuration. (C) 2008 Elsevier B.V. All rights reserved.