In this paper we compare the catalytic performance of ceria-supported gold and copper oxide catalysts for the preferential CO oxidation (PROX) in the presence of excess hydrogen. The catalytic properties are strongly affected by the synthesis procedure, i.e. deposition–precipitation (DP) and modified deposition–precipitation (MDP), mainly in the case of gold. The DP method leads to the preparation of more active PROX catalysts than the MDP one. Highly dispersed and more easily reducible gold or copper oxide species are formed on the catalyst surface and enhance the catalytic activity. Au/ceria catalysts are significantly more active, while CuO/ceria ones are remarkably more selective. The presence of CO₂ and H₂O causes a significant decrease in the catalytic activity, especially in the case of the gold catalyst. However, this deactivation is fully reversible. Both catalysts exhibit a perfectly constant behaviour with the reaction time.