The preferential oxidation of CO in rich hydrogen has been studied for CuO-CeO2-x catalysts. The catalysts were prepared by co-precipitation with K2CO3 + KOH as precipitators and characterized using N-2 physisorption isotherms, high resolution transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results indicate that nano-structured CUO-CeO2-x catalysts are obtained, and that the ratio of KOH/K2CO3 has a beneficial influence on the properties of CuO-CeO2-x catalysts, i.e., with the addition of KOH, the particle sizes grow smaller, CuO-CeO2-x catalysts have larger surface areas, CuO species in CuO-CeO2-x are more easily reduced and achieve higher catalytic performance in the preferential oxidation of CO in rich hydrogen. CO conversion higher than 99% with O-2 selectivity of 100% is obtained for CuO-CeO2-x catalysts with KOH/K2CO3 equal to 4:0 at a temperature of 90-110 degrees C and a space velocity of 30,000-120,000 ml g(-1) h(-1). (c) 2006 Elsevier B.V. All rights reserved.