To study anti-leukemic cell mechanism of quercetin, its effects on the proliferation activity of human leukemic cell (HL-60) in vitro were investigated by flow cytometric method and MTT assay.The studies indicated that quercetin showed strong suppression on the proliferation activity of leukmic cells in the time and dose-dependent manner. The value of IC50 and 95% confidence limit were 43. 1 (30. 5~60. 8)?mol/L after 48h. The flow cytometry indicated that it could induce programmed cell death of leukmia HL-60 ecll.