Carbonmonoxide oxidation mechanism was studied over the 50/50 Ag-Co and 50/50 Co-Ce mixed oxide catalysts. The temperature programmed methods (TPR-H(2) and TPD-CO) were used to characterize the catalysts. FTIR spectrums were collected under different feed conditions in order to determine the reaction mechanism. The carbonates adsorption bands and gas phase CO(2) bands were obtained for both of the catalysts. CO linearly bounded to Ag(+) sites at 2164 cm(-1) and to Co(3+) sites at 2105 cm(-1) for 50/50 Ag-Co mixed oxide catalyst. CO linearly bounded to Co(3+) sites at 2173 cm(-1) and 2108 cm(-1) for 50/50 Co-Ce mixed oxide catalyst. The CO adsorption studies showed that the CO reacted with surface oxygen species. The CO(2) adsorbed on the catalyst surface as surface carbonate species. The oxidation of CO with surface oxygen species is probably via a non-competitive Langmuir-Hinshelwood mechanism on the catalysts.