The influences of CeO2 microstructures on the structure and catalytic activity of supported Au nanoparticles in CO oxidation have been investigated in Au/CeO2/SiO2 catalysts. CeO2/SiO2 supports with various CeO2 microstructures were prepared and used to prepare Au/CeO2/SiO2 catalysts by deposition-precipitation using HAuCl4 as the precursor. Au(I) species and Au nanoparticles compete for the surface oxygen vacancies on CeO2 and highly dispersive CeO2 on SiO2 facilitates the formation of Au(I) species. Meanwhile, the presence of Au also facilitates the creation and stabilization of surface oxygen vacancies on CeO2. The Au nanoparticle-CeO2 interface plays an important role in the activity of Au/CeO2/SiO2 catalysts in CO oxidation. (C) 2009 Elsevier B.V. All rights reserved.