CuO-CeO2 catalyst precursors were synthesized by the homogeneous thermal decomposition of urea. Catalysts containing different Cu/Ce ratios were obtained by calcinating the precursors at 450 degrees C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM-EDX) and temperature-programmed reduction (TPR) measurements. Catalytic tests were performed in the temperature range 100-300 degrees C to evaluate the activity, selectivity and stability of these samples for the preferential oxidation of CO (CO PROX) reaction. The effect of the presence of H2O and/or CO2 in the feed stream on both the structure and the catalytic behaviour of the samples were also analysed. The catalytic activity of the samples for both CO and H-2 oxidation reactions increases as the copper loading increases and H-2 oxidation competition becomes more important when the available oxygen in the gas phase is scarce. During the first 24 h of CO PROX operation, catalysts with low copper content are perfectly stable but the sample with the highest copper content has shown an irreversible deactivation, probably due to a partial reduction of the segregated CuO phase present in the fresh sample. The presence of both water and carbon dioxide in the feed gas stream has a negative effect on the catalytic activity of CuO-CeO2 catalysts. (C) 2007 Elsevier B.V. All rights reserved.