CuO supported on CeO 2, Ce 0.8 Zr 0.2 O 2 and Ce 0.8 Al 0.2 O 2 based catalysts (6%wt Cu) were synthesized and tested in the preferential oxidation of CO in a H 2 -rich stream (CO-PROX). Nanocrystalline supports, CeO 2 and solid solutions of modified CeO 2 with zirconium and aluminum were prepared by a freeze-drying method. CuO was supported by incipient wetness impregnation and calcination at 400 °C. All catalysts exhibit high activity in the CO-PROX reaction and selectivity to CO 2 at low reaction temperature, being the catalyst supported on CeO 2 the more active and stable. The influence of the presence of CO 2 and H 2 O was also studied.