The mechanical mixing of Mn2O3 or CeO2 to Ce-ZSM-5 considerably enhanced the rate of the reduction of NO by propene in the low to medium temperature region, although Mn2O3 or CeO2 itself was much less active for this reaction. In contrast, Mn2O3 was highly active and CeO2 was moderately active for the oxidation of NO to NO2. On the basis of the comparison of the rates of the C3H6 + O2, NO + C3H6 + O2 and NO2 + C3H6 + O2 reactions over these catalysts, a bifunctional mechanism is proposed, in which Mn2O3 and CeO2 accelerate the oxidation of NO and the subsequent reaction steps between NO2 and propene proceed on Ce-ZSM-5.