The influence of cocations (Cr and Ag) on the activity of Cu/CeO2 catalysts in the selective reduction of NOx with C3H6 has been investigated in this study. The reduction of NOx under lean conditions was greatly improved by loading Cr and Ag onto a Cu/CeO2 catalytic system. All the synthesized bimetal catalysts were characterized using XRD and TPR-H-2. The better metal-support interaction and metal dispersion shown by Cu/Ag/CeO2 have elevated its performance compared to the Cu/Cr/CeO2 catalyst. By having such salient features, the competitiveness factor (SSCR-HC) assigned by Cu/Ag/CeO2 was generally better than that of the other tested catalysts. The presence of O-2 was proven to be a very crucial factor for promoting the selective reduction of NOx with C3H6. (C) 2003 Published by Elsevier Inc.