We have found that physical mixing (solid grinding, SG) of dimethylgold(III) acetylacetonate (Me 2 Au(acac)) adsorbed on SiO2 with potassium t-butoxide ((KOBu)-Bu-t) significantly improved the catalytic activity for CO oxidation at low temperature, and T-1/2 (the temperature at 50% CO conversion) became extremely low such as -43 degrees C. We have also developed an alternative Au complex for SG, and 2-(p-tolyl)pyridinebis(trifluoroacetate) gold(III) (AuTFA) could be adsorbed on metal oxide (MOx) supports by physical mixing of AuTFA with MOx in air at room temperature for 20 min, and small Au nanoparticles (NPs) were deposited after calcination. The sizes of Au NPs were almost the same as those prepared using Me2Au(acac) and smaller than those prepared by DP for Al2O3 and TiO2 supports. In addition, grinding AuTFA adsorbed on SiO2 with (KOBu)-Bu-t was also effective for reducing the size of Au particles and gave Au clusters with a mean diameter of 2.2 nm. Moreover, Au/Al2O3 and Au/K-SiO2 exhibited high catalytic activity for CO oxidation under simulated real exhaust gas conditions (low CO concentration and high humidity up to 100% relative humidity) at ambient temperature.