Abstract A FTIR study of the CO oxidation on Au/ZnO from 90 to 300 K in the absence and in the presence of hydrogen has been performed. An insight on the origin of deactivation during CO oxidation at room temperature and on the regeneration effect of hydrogen is given. FTIR spectra show that at 90 K only carbonylic species on the metallic particles and on the support cations are produced. Carbonates and/or carbonyls at the interface between the metal and the oxide are produced by increasing the temperature from 90 to 300 K. The presence of hydrogen in the mixture inhibits in some extent the formation of transient intermediates and of stable carbonates adsorbed on the support. The amount of stable species at the interface is reduced as a consequence of the lowered basicity of the reactive oxygen species at the borderline between the metal and the oxide.