Adsorption properties of silver monolayer and bilayer deposited at underpotentials on a Pt(111) electrode were studied by means of linear sweep voltammetry, in situ surface X-ray scattering and infrared spectroelectrochemistry. Surface X-ray scattering measurements show a pseudomorphic Ag monolayer and an incommensurate expanded bilayer on Pt(111) formed at underpotentials. Unusual adsorption properties of the silver layers with respect to the bulk silver are observed. The two AE adlayers were found to have intermediate adsorption/oxidation characteristics between those of metallic Ag and Pt surfaces with (111) orientation. The Ag monolayer has properties that facilitate adsorption of bisulfate anions and adsorption and oxidation of CO. These properties are closer to the adsorption properties of the Pt(111) surface than to those of Ag(111), which adsorbs sulfate anions and does not adsorb CO. The Ag bilayer on the Pt(111) surface adsorbs sulfate anions as AE(111) does, but in contrast to the behavior of Ag(111), it adsorbs CO. These properties of the Ag adlayers appear to be a consequence of the charge-transfer process and the electron distribution in the Ag/Pt(111) surface.