To investigate the influence of sodium valproate (VPA) on proliferation, apoptosis and differentiation of HL-60 cell line, effect of VPA in various concentrations on proliferation of HL-60 cells was detected by MMT; Wright-Giemsa staining was performed to observe the morphologic changes of HL-60 cells; NBT experiment was used to test the differentiation of HL-60 cells; flow cytometry was used to observe cell cycles and analyze the apoptosis. The results indicated that the changes of the growth curve showed inhibition of proliferation of HL-60 cells. After a 24-48 hours culture with 2 mmol/L VPA, the cells exhibited nuclear shrinkage, pyknosis fragmentation and appearance of apoptosis bodies. The percentage of the annexin V(+)/PI(-) cells which were apoptotic increased from 2.9% to 17.1%; hypodiploid peak was observed; the percentage of HL-60 cells in G(1) phase increased from 51.1% to 84.6% and the cells in S phase decreased from 37.9% to 14.4%. After a week culture with 0.25 mmol/L VPA, the cells exhibited characteristics of differentiation. The percentage of NBT positive cells was (47 +/- 2)%. It is concluded that VPA can inhibit the proliferation of HL-60 cells while inducing differentiation and apoptosis of these cells. The mechanism needs to be further studied.