Objective:To investigate the effect of total flavonoids of Hedysarum polybotry on the proliferation, cell cycle,and expressions of p21~(Ras) and proliferating cell nuclear antigen(PCNA) gene in erythroleukemia cell line K562.Methods:The effect of total flavonoids of Hedysarum polybotry on K562 cell line survival was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium(MTT) reduction assay.The time-and dosedependent manner was also observed.The cell cycle and apoptosis were analyzed with flow cytometry(FCM). The immunocytochemistry method was applied to quantitatively analyze the effects of flavonoids of Hedysarum polybotry on changes p21~(Ras) and PCNA gene expressions.Results:Flavonoids of Hedysarum polybotry(20-100μg/mL) significantly inhibited the proliferation of K562 cells in a time-and dose-dependent manner.After K562 cells were cultured for 48 h,total flavonoids of Hedysarum polybotry had no significant effect on the apoptosis of K562 cells but showed significantly inhibition(P<0.01),indicating that total flavonoids of Hedysarum polybotry could induce K562 cells arrested at G_0/G_1 and G_2/M phases.Compared with the control group,p21~(Ras) and PCNA gene expressions were decreased significantly in K562 cells treated with total flavonoids of Hedysarum polybotry(40 and 80μg/mL,respectively) for 48 h.Conclusion:The inhibitory effect on proliferation of K562 cells was observed in the groups treated with flavonoids of Hedysarum polybotry,which might be related to cells arresting. Objective: To investigate the effect of total flavonoids of Hedysarum polybotry on the proliferation, cell cycle, and expressions of p21 ~ (Ras) and proliferating cell nuclear antigen (PCNA) gene in erythroleukemia cell line K562. Methods: The effect of total flavonoids of Hedysarum polybotry on K562 cell line survival was determined by the 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium (MTT) reduction assay.The time-and dose dependent manner was also observed. The cell cycle and The immunocytochemistry method was applied to quantitatively analyze the effects of flavonoids of Hedysarum polybotry on changes p21 ~ (Ras) and PCNA gene expressions. Results: Flavonoids of Hedysarum polybotry (20-100 μg / mL) significantly inhibited the proliferation of K562 cells in a time-and dose-dependent manner. After K562 cells were cultured for 48 h, total flavonoids of Hedysarum polybotry had no significant effect on the apoptosis of K562 cells but for a significant antly inhibition (P <0.01), indicating that total flavonoids of Hedysarum polybotry could induce K562 cells arrested at G_0 / G_1 and G_2 / M phases. Compared with the control group, p21 ~ (Ras) and PCNA gene expressions were decreased significantly in K562 cells treated with total flavonoids of Hedysarum polybotry (40 and 80 μg / mL, respectively) for 48 h. Confluence: The inhibitory effect on proliferation of K562 cells was observed in the groups treated with flavonoids of Hedysarum polybotry, which might be related to cells arresting .