Summary: Some biological characteristics of human bone marrow mesenchymal stem cells (MSCs) cultured in vitro were observed. hMSCs were isolated from bone marrow and purified by density gradient centrifugation method, and then cultured in vitro. The proliferation and growth characteristics of hMSCs were observed in primary and passage culture. MSCs of passage 3 were examined for the purify by positive rate of CD29 and CD44 through flow cytometry. Human bone marrow MSCs showed active proliferation capacity in vitro. The purify of MSCs separated by our method was higher than 90 %. It was concluded that hMSCs have been successfully cultured and expanded effectively. It provided a foundation for further investigation and application of MSCs.