Abstract: In order to investigate the influences of activated carbon quantity in cigarette filter on the release of some harmful components in mainstream cigarette smoke, cigarette filters with activated carbon added at 0, 1, 2, 3, 4 mg/mm were prepared. Ion molecule reaction mass spectrometry (IMR-MS) coupled with an RM20H rotary smoking machine was adopted for on-line determination of nitrogen oxides, alkenes, benzene series, aldehydes and ketones on puff-by-puff basis. The results showed that: 1) When added at 3 or 4 mg/mm, the total release of the above harmful components in mainstream cigarette smoke were decreased by 8%-62%. 2) There was an“ignition (or the so-called 1st puff high) effect”for the release of isoprene, 1,3-butadiene and benzene, generally their release in mainstream smoke decreased post first puff then increased slowly with the proceeding puffs. 3) For unperforated filter cigarettes, these reduction effects of activated carbon were more pronounced at the addition of 3 mg/mm, and the total release of the harmful components in mainstream smoke was decreased by 21%-61%. For perforated filter cigarettes, the puff-by-puff release of the target analytes in mainstream smoke was lower at the addition of 4 mg/mm, and the total release of toluene, aldehydes and ketones decreased by 34%-62%.