Modification of cobaltic oxide (obtained from the reduction of high-valence cobalt oxide and assigned as R230, S-BET = 100 m(2) g(-1)) with different loading of ceria was proceeded using the impregnation method (assigned as CeX/R230, X = 4, 12, 20, 35 and 50 wt%). The Cex/R230 catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption at -196 degrees C, temperature-programmed reduction (TPR) and transmission electron microscopy (TEM). Their catalytic activities towards the CO oxidation were studied in a continuous flow micro-reactor. The results revealed that the optimal modification, i.e., Ce20/R230, can increase the surface area (SBET = log m(2) g(-1)) of cobaltic oxide, further weaken the bond strength of Co-O and lower the activation of CO oxidation among CeX/R230 catalysts due to the combined effect of cobaltic oxide and ceria. The Ce20/R230 catalyst exhibited the best catalytic activity in CO oxidation with T-50 (temperature for 50% CO conversion) at 88 degrees C. (C) 2007 Elsevier B.V. All rights reserved.