In a fixed bed reactor with a quartz tube, the effects of the concentration of CO2 in the feed gas on the uncatalyzed reaction between soot produced in a natural gas diffusion flame and NO were investigated. They were compared with CO2 effects on reactions involving candle soot and bituminous coal char. The presence Of CO2 in the feed gas exerted no influence on the reaction of NO with natural gas soot. However, it did result in a lower initial temperature in the reaction of candle soot or coal char with NO, and separated the whole initial reaction process into two stages. At higher CO2 concentrations, more NO reduction occurred in the reaction with candle soot or coal char during the initial reaction process. However, no dramatic changes in the amount of NO reduction were observed for natural gas soot. The addition Of CO2 seemed to have no effect on the apparent activation energy of the NO-natural gas soot reaction, while a lowering of the apparent activation energy was observed in the reaction of NO with candle soot or coal char as the CO2 concentration increased. The abundant C(O) complexes formed during sample gasification by CO2 were assumed to play an important role in the enhancement of the reaction.