Abstract: Objective To observe the effect of hypoxic preconditioning on the biological function of bone marrow-derived endothelial progenitor cells(BM-EPCs). Methods Mononuclear cells were collected by density gradient centfifugation from the bone marrow of rats. The isolated cells were cultivated in dishes coated with the vitronectin from rat plasma，filled with the endothelial cell basal medium-2. First，All of the cells were cultured under the conventional culture conditions (37 ℃ and 5% CO2) . After four days ，cultured cells were divided into control group and hypoxia training groups. Cells of the control group were cultured in previous conditions for another three days. However, cells of the hypoxia training groups were cultured in previous conditions for 0 days、1 days、2 days，then，under the hypoxic condition (1% O2+5% CO2+94% N2) for another 72 hours、48 hours、and 24 hours，respectively. In the seventh days，all of the groups were collected for the following study，immunofluorescence labeling and cell analyzer were used to indentify BM-EPCs. the tube formation of BM-EPCs were tested by matrigel assay. Apoptosis of BM-EPCs were assayed by Annexin V/PI antiapoptotic assay. So as to explore the hypoxic conditions on the function of BM-EPCs, for the best time to hypoxic. Results As the hypoxic time extended，The early apoptosis rate was significantly increased. There was no significantly difference between the control group（0.89±0.20） and the hypoxic 24 hours group（1.33±0.07）（P＞0.05）. Compare with the control group ，The tube formation of the hypoxic 24 hours group was stronged significantly (P＜0.01). Conclusion After hypoxic preconditioning BM-EPCs for 24 hours, the rate of apoptosis was not obvious, but the tube formation ability was markedly increased.

Key words: hypoxic preconditioning, Endothelial cells, Stem Cells, Tube formation, Apoptosis