Objective To study the changes of surface markers of endothelial progenitor cell during differntiation into endothelial cells. Methods Mononuclear blood cells(PBMC) were isolated from rat peripheral blood by means of Ficoll density gradient centrifugation and cultured in the presence of VEGF and bFGF.Expressions of CD31,CD34,Flk-1 and vWF on adherent cells were assayed with immunochemistry technique. Results The expressions of CD31,CD34,Flk-1 and vWF on adherent cells changes during the culture peroid.The percentage of CD31 and CD34 expressions decreased gradually.On the 6th day of culture,the expressions of CD31 and CD34 completely disappeared.The appearance of Flk-1 and vWF on adherent cells increased gradually,and reached 100% expression on the 7th day of culture. Conclusion The differentiation of endothelial progenitor cells into endothelial cells was characterized by the appearance of endothelial cell markers and disappearance of stem cell markers,both in a way of gradual progression.