Aim To study the apoptosis effect of Sir-aitia grosvenorii extract on human lung cancer cells A549 and its mechanisms.Methods MTT assay was applied to determine A549 cell proliferation.Hoechst 33258 staining was applied to investigate morphological changes in A549 cells.To find out the cause of cell growth inhibition,several experiments on cell cycle distribution and apoptosis were performed by flow cy-tometry analysis.The expression of p21 and Bcl-2 was determined by Western blot.Results Flow cytometry analysis showed that treatment with mogrol arrested A549 cells in the G0 /G1 phase and induced apoptosis. After treatment with Siraitia grosvenorii extract,West-ern blot experiment showed cell cycle regulator p21 was up-regulaed,while the apoptosis inhibitor Bcl-2 was down-regulated.Conclusion Treatment with Siraitia grosvenorii extract arrests the A549 cells at G0 /G1 phase and induces apoptosis that may contribute to the anti-proliferation activity of mogrol through the regula-tion of p21 and Bcl-2 expression.