Three types of supported cobalt catalysts (CoOx/SiO2, CoOx/TiO2 and CoOx/Al2O3) were prepared by incipient wetness impregnation with aqueous Co(NO3)(2)center dot 6H(2)O solution. The phase composition and the interactions of cobalt with supports under different calcined temperatures were investigated using thermogravimetry (TG), N-2-adsorption at -196 degrees C, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and diffuse reflectance spectroscopy (DRS). Their catalytic activities towards the CO oxidation were further studied in a continuous flow micro-reactor. The results showed that the interaction of cobalt oxide with supports was much stronger in the kinds of Al2O3 and TiO2, while no conclusive evidence of any interaction was found for SiO2. Besides the crystalline Co3O4 which was formed in three supported catalysts, both high-temperature phases CoAl2O4 and CoTiO3 spinel were also detected under XRD, DRS and TPR analysis. The degree of interaction between cobalt oxide and the support not only affected the surface area and reduction behavior of the catalysts, the catalytic activity toward the CO oxidation also affected simultaneously. As the CoAl2O4 and CoTiO3 spinel formed, both the surface area and catalytic activity decreased significantly.