The composites with nanosized gold loaded in nanoporous ceria were prepared on a large scale by a facial and environment-benign sol-gel process, These materials were characterized by XRD, ICP, BET, UV-vis absorption. XPS, HRTEM and EDX The main factors such as size and surface state of the Au and defect in the ceria could be adjusted by acid treatment of the composites in ascorbic acid solution to improve the activity and decrease the content of noble metal Au in the materials. Enhanced catalytic activities were obtained for the CO oxidation reaction over the catalysts due to the small crystal sizes with narrow size distributions of gold nanoparticles, a large amount of defects in the nanoporous ceria support, as well as a high ratio of Au3(+)/Au-0 in the nanocomposites. (C) 2008 Elsevier B.V. All rights reserved.