CeCucontaining catalyst (CeCuMgAl(O)) was prepared by coprecipitation whose catalytic activity for NO+CO in the presence of oxygen was examined and compared with the catalyst free of cerium.The effect of H 2O on the catalytic activity was also investigated.The results show that for NO+CO reaction in the presence of oxygen,the activitytemperaturewindow of CeCuMgAl(O) shifts to lower temperature than that of CuMgAl(O).The presence of H 2O gives rise to the significant changes of catalytic activity of these two catalysts in low temperature region:great reducing for CuMgAl(O) and intensive increase for CuCeMgAl(O) whereas no obvious effect in high temperature region.The synergy between CuCe oxides and thus much more Cu+ exist in the CeCuMgAl(O) than CuMgAl(O) are responsible for these differences.