The interest in studying silver dispersed onto various supports has been first of all fueled by the unique catalytic activity of silver in the ethylene epoxidation reaction [1]. Finely dispersed silver catalysts have been recently shown to have high activity in lowtemperature [2] and selective [3] oxidation of CO in hydrogen excess. At the same time, silver nanoparticles exhibit unique optical properties caused by surface plasmon resonance (SPR) observed as an absorption maximum in the visible spectral region. The SPR position of silver nanoparticles can be varied in a wide frequency range by varying their size and shape [4] and the dielectric constant of decorating materials used [5, 6]. In the present work, the SPR of oxidesupported silver nanoparticles was studied. It was demonstrated that oxygen adsorption (formation of an oxide film) had an effect on the SPR position of fine silver nanoparticles.