Recent X-ray photoelectron spectrometer(XPS) analysis of Au powder synthesized by evaporating high purity gold metal (> 99.99%) in an inert gas detected impurity metals such as Ag and In at levels which far exceed those expected from the impurity levels of raw gold metal. Several samples of Au powder containing different amount of impurity metals were prepared to examine whether the activity of the Au powder for CO oxidation depends upon the impurity or not. The activity of the powder showed a strong correlation with the surface concentration of Ag.