OBJECTIVE To investigate the effect of ecdysterone (EDS) on the proliferation of human bone marrow mesenchymal stem cells (hMSCs) in vitro. METHODS hMSCs were isolated from human bone marrow cell suspension by density gradient centrifugation. The expression of integrins CD44, CD105, CD34 and CD29 were examined by immunocytochemical method. EDS at 10, 25, 50 or 100 microg/ml were added in hMSC culture system, using the routine culture medium for hMSCs as control. The cell viability were analyzed by MTT assay and the cell cycle changes were examined by flow cytometry. RESULTS The optical density (OD) differed significant between the EDS treatment groups and the control group (P<0.01), and 25 microg/ml EDS group showed the highest OD value (P<0.01) without significant differences among 10, 50 and 100 microg/ml EDS groups (P>0.05). Flow cytometry showed that treatment of the cells with 25 microg/ml EDS significantly increased the cell percentages in S and G(2)M phases and the proliferation index (PI) of the cells as compared with the control group. CONCLUSIONS Within a given concentration range, EDS can promote the proliferation of hMSCs in vitro, and this effect can be the most obvious at the concentration of 25 microg/ml. The effect of EDS in promoting the proliferation of hMSCs does not positively correlate to EDS concentration administered.