Abstract: In order to study the changes of chemical constituents in cut tobacco before and after CO₂ expansion, the free amino acids in 6 kinds of cut tobacco from different producing areas and different stalk positions were ultrasonically extracted with ultrapure water at room temperature for an hour, then reacted with a deriving reagent, AQC, and analyzed qualitatively and quantitatively by reversed-phase high performance liquid chromatography, sixteen free amino acids were found.The results showed that after CO₂ expansion, the contents of proline, serine, glutamic acid, glycine, histidine and isoleucine generally assumed a descending tendency, while the contents of arginine and aspartic acid tended to increase.Except that in the lower leaves of Fujian ZO1, the total f ree amino acids in expanded cut tobacco somewhat reduced, the reduction was relatively obvious in Fujian B3F and Fujian BO1.