Abstract: Objective To study the effect of Herba Saginae Japonicae ethanol extract (HSJ) on the differentiation of human promyelocytic leukemia (HL-60) cells.Methods After 24 hours' incubation during logarithmic growth phase,the HL-60 cells were assigned into three experimental groups (treated with 250,125,62.5μg/mL HSJ),a positive control group (with 100 μg/mL pirarubicin),and a negative control group.The proliferation of HL-60 cells was detected with methyl thiazolyl tetrazolium bromide (MTT) assay;the cell morphology was observed with Wright-Giemsa staining; the cell differentiation ability was determined with nitroblue tetrazolium (NBT) reduction assay; the expressions of differentiation related antigen (CD11b and CD14) were measured with flow cytometry (FCM);and the expression of c-myc protein was detected with Western blot.Results Compared with the control group,the HSJ-treated HL-60 cells demonstrated apparent differentiation and inhibited proliferation,with decreased nucleus and cytoplasm ratios and kidney-or broad bean-shaped nucleoli.For the HSJ cells treated with 250,125,and 62.5 μg/mL HSJ,the NBT reduction rates were 16.67±1.76%,10.83±1.26%,and 6.00±0.87%;the CD11b positive rates were 66.77±4.27%,52.27±0.95%,and 46.27±0.38%; and the CD14 positive rates were 96.63±0.23%,85.25±3.80%,and 63.84±0.78%,respectively; all the indicators were significantly increased compared to those of negative control HSJ cells (0.83±0.29%,41.13±0.42%,and 53.30±7.23%)(P<0.05 for all).Wheaeas,the c-myc protein expressions (0.38±0.01,0.45±0.01,and 0.58±0.02) of the HL-60 cells treated with different dosages of HSJ decreased significantly compared to that (0.71±0.02) of the negative control HSJ cells (P<0.05).Conclusion HSJ can induce HL-60 cells differentiating into mature granulocytes or monocytes.