Silver, cobalt and ceria mixed oxide catalysts were prepared at different metal/metal oxide molar ratios by the co-precipitation method, calcined at different temperatures (200 degrees C, 450 degrees C) and tested for the selective CO oxidation reaction in H-2 rich gas stream. XRD, XPS, N-2 physisorption, SEM and TPR-H-2 techniques were used to characterize the catalysts. Catalysts have an average pore diameter in the mesoporous range. Catalysts which were calcined at 200 degrees C had amorphous phase structure. After calcination at 450 degrees C, not only the crystal phase structure but also decrease in BET surface areas of the catalysts and the shift at light off temperatures of the catalysts to the higher temperatures were obtained. The highest activity and selectivity was obtained from the catalysts calcined 200 degrees C which were 50/50 Ag-Co and 50/50 Co-Ce mixed oxide catalysts, respectively, which did not loose their activity and selectivity in a reaction period of 5800 mm. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.