Abstract: A chemiluminescent method for determining nitrogen oxides (NO_x) in mainstream cigarette smoke was deliberated.The gas phase of mainstream smoke filtered by Cambridge pad was directed into an evacuated mixing chamber puff by puff, and then NO_x was determined by an NO_x analyzer according to the chemiluminescent theory. The CV of this method was below 5% and the recovery of NO_x was over 98%.Two components, nitrogen monoxide (NO) and nitrogen dioxide (NO₂), in mainstream smoke of six brands of cigarettes were determined with an external standard method.It was concluded that this method had high repeatability and recovery, it was faster and suitable for the analysis of NO_x in mainstream smoke.