The spectro-electrochemical behavior of carbonate and bicarbonate ions at the Au(111) electrode surface was studied using the infrared reflection absorption spectroscopy (IRAS). An absorption band caused by the adsorbed carbonate ions was observed in the wavenumber region of 1425-1511 cm(-1) both in Na2CO3 and NaHCO3 solutions. It was concluded that the adsorbed carbonate ions co-ordinate with the electrode surface in the unidentate state with their symmetry axis normal to the substrate. This orientation is retained in the whole potential region where carbonate ions adsorb on the electrode surface in contrast to the behavior of the carbonate ions adsorbed on the Pt(111) electrode surface.