The solid solutions of CexSn1-xO2 incorporated with alumina to form CexSn1-xO2-Al2O3 mixed oxides, by the suspension/co-precipitation method, were used to prepare CuO/ CexSn1-xO2-Al2O3 catalysts for the selective oxidation of CO in excess hydrogen. Incorporating Al2O3 increased the dispersion of CexSn1-xO2, but did not change their main structures and did not weaken their redox properties. Doping Sn4+ into CeO2 increased the mobility of lattice oxygen and enhanced the activity of the 7%CuO/CexSn1-xO2-Al2O3 catalyst in the selective oxidation of CO. The selective oxidation of CO was weakened as the doped fraction of Sn4+ exceeded 0.5. Incorporating appropriate amounts of Sn4+ and Al2O3 could obtain good candidates 7%CuO/CexSn1-xO2-Al2O3(20%), 1-x = 0.1-0.5, for a preferential oxidation (PROX) unit in a polymer electrolyte membrane fuel cell system for removing CO. Its activity was comparable with, and its selectivity was much larger than, that of the noble catalyst 5%Pt/Al2O3. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.