A high-valance cobalt oxide, CoOx, was prepared from cobalt nitrate aqueous solution through precipitation with sodium hydroxide and oxidation by hydrogen peroxide. Further, other pure cobalt oxide species were refined from the CoOx by temperature-programmed reduction (TPR) to 170, 230 and 300 degreesC. They were characterized by TPR and X-ray diffraction (XRD). Adsorption of CO and the co-adsorption of CO/O-2 over the cobalt oxides were further tested by in situ FTIR. It was shown that Co3O4 is quite active for the oxidation of CO at room temperature in the presence of oxygen, leading to the formation of CO2. The variation in the oxidation of CO was interpreted with a mechanism involving two kinds of oxygen species, i.e., *-O-2 on the CoOx surface and *-O-L on the surface of Co3O4 spinel structure.