CO adsorption on gold particles deposited on well-ordered alumina and iron oxide films was studied with temperature-programmed desorption. Scanning tunneling microscopy was used to provide correlative structural characterization. The results show that the adsorption of CO on gold exhibits a size effect in that small particles adsorb CO more strongly. For a given particle size (similar to3 nm), CO desorption temperature (at similar to170 K) is essentially independent of the supports studied. Therefore, support effects seen in CO oxidation on real catalytic systems must arise from he interaction of oxygen rather than CO with these catalysts.