Objective:To investigate whether rat bone marrow－derived mesenchymal stem cells(BMSCs) could spontaneously differentiate into endothelial cells in normal culture condition. Methods:Primary rat BMSCs were separated and cultured to passage 7. The passage 3 and passage 7 BMSCs were prepared for this experiment. The expression of endothelial cell markers CD31,tyrosine kinase with immunoglobulin－like and EGF－like domains 2 (Tie－2) and von Willebrand factor (vWF) in passage 3 and passage 7 BMSCs were determined by Real－time PCR,and the ability of angiogenesis were determined by an in vitro angiogenesis kit (Matrigel). Futhermore,the expression of vWF protein in BMSCs were detected using immunofluorescence staining. Results:After normal cultured to passage 7,BMSCs partly formed an oval shape. Real－time PCR and immunofluorescence showed that the expression of endothelial cell markers were significantly higher in passage 7 BMSCs than in passage 3 BMSCs. In vitro angiogenesis experiments showed that passage 7 BMSCs could form a mesh structure in matrigel. Conclusion:BMSCs in normal culture condition changed their phenotypes,and could partially differentiate into endothelial cells spontaneously.