Microwave reactor with the mixture of ammonium bicarbonate (NH4HCO3) and Ga-A zeolites was set up to study the removal of nitrogen oxides (NOx) from waste gas with excess oxygen concentration (14-19%) at low temperature (80-120 degrees C). The results showed that the microwave reactor filled with NH4HCO3 and Ga-A zeolites could reduce NOx to nitrogen with the best purifying efficiency of 95.45% and the best denitrification amount of 89.28 mg h(-1). The optimal microwave power and residence time (RT) on denitrification was 259-280 W and 0.259s, respectively. Microwave denitrification effect of the experiment using ammonium bicarbonate and Ga-A zeolites was much higher than that using ammonium bicarbonate or Ga-A zeolites only. The mechanism for microwave-induced NOx reduction can be explained as the microwave-induced catalytic reaction between NOx and ammonium bicarbonate with Ga-A zeolites being the catalyst and microwave absorbent. (c) 2006 Elsevier Ltd. All rights reserved.