Abstract: In order to clarify the contribution of proline to chemical components in mainstream cigarette smoke, ¹⁵N-labeled and non-labeled proline were added into cut tobacco, and the qualitative and dose-effect relationships between proline and mainstream cigarette smoke components were studied in gas phase and particulate phase mainstream cigarette smoke by GC/MS. The results showed that:1) Proline in cut tobacco contributed to the formation of pyrrole, 1-methyl-1H-pyrrole, 2-pyrrolidinone, 1-(1H-pyrrol-2-yl)ethanone, pyrazine and 1-pyrrolidinylacetonitrile. 2) The contribution rate of proline to the formation of 1-pyrrolidinylacetonitrile in mainstream cigarette smoke was 65%, and to that of pyrrole and 1-(1H-pyrrol-2-yl)-ethanone were 36% and 12%, respectively. The contribution rates of proline to the formation of 1-methyl-1H-pyrrole, pyrazine, and 2-pyrrolidinone were less than 10%.