Objective:To study the effect of cardiomyocyte microenviroment in vitro on bone marrow mesenchymal stem cell(MSCs) in diffierentiating into cardiomyogenic cell. Methods:Bone marrow cells were isolated form SD rat’s leg bone by their adherence to plastic in vitro,the MSCs were purified by culture-expanded and passaged. After treaded with DNA demethylating agent 5-azacytidine(5-aza). In experiment group the MCSs were grown,which were cultured in dishes seeded with cardiomyocytes from neonatal rats. In control group the MSCs were cultured only. The MSCs differentiation was observed by microscope,immunohistochemistry staining for Demin and cardiac troponin I(cTnI),and the positive time were observed. Results:In control group,after treated with 5-aza for 10 days,the clones of adhenrent fibroblast-like cells were formed,and they connected with adjoining cells 15 days and formed myotube-like structures about 20 days later. But the experiment group they formed myotube-like structures after about 17 days. The results of immunohistochemistry staining indiated that the experiment group’s positive time was earlier than the control group’s. Conclusion:The cardiomyocyte microenviroment are thought to be a key factor in inducing bone marrow mesenchymal stem cells to differentiate into cardiomyogenic cells.