Oxygen adsorption on silica-supported gold catalyst from NO2 and O-2 exposures were investigated by temperature-programmed desorption spectroscopy under a vacuum condition. NO2 and O-2 exposures of the surface of the catalyst at room temperature gave adsorbed oxygen in atomic state. Adsorbed oxygen penetrated beneath the gold with lower activation energy for NO2 exposure than for O-2 exposure. Adsorbed oxygen in oxidic state which was desorbed above 600 K altered the surface properties of gold and resulted in the decrease of activation energy for oxygen to penetrate beneath the gold surface.