Microwave discharge-assisted reduction of NO by CH4 in the presence of excess O-2 over Co/HZSM-5 and Ni/HZSM-5 catalysts was studied. By comparing the activities of the catalysts in the microwave discharge mode with that in the conventional reaction mode, it is demonstrated that microwave discharge enhanced greatly the conversion of NO to N-2, and expanded the reaction temperature range of the catalysts. For the Co/HZSM-5 catalyst, the conversion of NO to N-2 increased by 30%, and the optimum temperature decreased by 200 degreesC. With the Ni/HZSM-5 catalyst, the highest activity was close to 100%, and the optimum temperature decreased by 325 degreesC. The conversion of CH4 also increased in the microwave discharge mode over both of the catalysts.