Abstract: In order to identify the main precursors of ammonia (NH₃) in cigarette smoke,the yield of NH₃ from the main nitrogen-containing compounds in tobacco was studied by a smoking simulator in the presence of tobacco matrix. The main precursors were selected by referring to their contents in tobacco and validated by smoking experiments to investigate the dose-effect relationships between the yield of NH₃ in mainstream and sidestream smoke and the addition amounts of precursors. The results showed that the main precursors of ammonia in cigarette smoke were protein, asparagine, ammonium salt and proline, and their contribution rates to NH₃ in cigarette smoke were 65.41%, 15.96%, 13.46% and 11.26%, respectively.