Objective  To establish a new and effective method of purifying rat bone marrow mesenchymal stem cells (BMSCs) in vitro and to study the biological behaviors of the cultured cells.    Methods  BMSCs were cultured by whole bone marrow culture method. To identify BMSCs

the experiments of adipogenic and osteogenic differentiation were carried out and flow cytometry was employed to detect surface antigens. The cells were purified by planting in lower density (3×10

2

/cm

2

) and by erasing the peripheral large-and-flattened cells that surrounded the “colon

y”. The biological behaviors of these cells such as colony-forming-unit test

growth curve

and cell cycle analysis were further compared to those planted in a higher density (3×10

4

/cm

2

).     Results  BMSCs were successfully cultured by whole bone marrow method

and they could be induced into adipocytes and osteocytes in vitro. Flow cytometry demonstrated that the expressions of CD34 and CD45 were lower than 2%

and those of CD73 and CD90 were more than 95%. Furthermore

the purified cells showed stronger stemness features during their growth. The efficacy of CFU test was (28.80±5.00)% (P0.01). The cell amount of those cultured for 12 d was increased by 26.18±4.80 times (P0.05). The percentage of the cells at S+G

2

/M phase was (45.98±1.60)% (P0.01).     Conclusion  More purified BMSCs are obtained by culturing cells in lower density combining with erasing peripheral large-and-flattened cells

and the cells have better biological properties.