The influence of the surface area, crystal size of the support and the Cu loading (3-9 wt.%) on the catalytic behavior of CuO/CeO 2 catalysts was investigated in the preferential CO oxidation (PROX) reaction. Two ceria samples were used: a high-surface area one (SCe) prepared by the templating technique and a low surface commercial one (ACe). Copper was incorporated to the calcined support by classical impregnation. Techniques were used to characterize the textural, structural and chemical properties of the catalysts (BET, XRD, HRTEM, and TPR). For catalysts supported on SCe these techniques evidenced highly dispersed copper species in strong interaction with nanosized CeO 2 crystals. The enhanced redox properties of the CuO-support interface sites at low temperature evidenced by TPR in CuSCe catalysts play a fundamental role in the catalytic behavior for the CO oxidation in presence of excess H 2 (PROX). CuSCe catalysts showed excellent catalytic activity compared to catalysts supported on the commercial CeO 2 . Total conversion of CO is obtained at 125 8C with 100% selectivity to CO 2 . In the presence of CO 2 and H 2 O the maximum CO conversion for temperatures higher than 125 8C was 95%. Selectivity also decreased being more pronounced when H 2 O was present. This negative effect was reversible since the original activity and selectivity were practically restored upon elimination of these components from the feed. Partially reduced Cu + species seem to be present in the catalysts according to CO adsorption followed by DRIFT.