In order to clarify the support effect on CO oxidation over Au catalysts without the influence of the size effect of Au, An Was deposited on a variety of supports with high dispersion by gas-phase grafting (GG) of an organo-gold complex. Comparison of Au/SiO2 with Au/Al2O3 and Au/TiO2, which were prepared by both GG and liquid-phase methods and were active for CO oxidation at 273 K, showed that there were no appreciable differences in their catalytic activities as far as Au. is deposited as nanoparticles with strong interaction. However, Au deposited onto the acidic supports, such as silica-alumina and activated carbon (AC), exhibited a much lower CO oxidation catalytic activity than those of the active Au catalysts, such as Au/TiO2. (C) 2003 Elsevier Science B.V. All rights reserved.