INTRODUCTION There is paucity of information whether umbilical cord derived mesenchymal stem cells (UCMSCs) from different donor might have different biologic characteristics and effects on improving myocardial repair after myocardial infarction (MI). METHODS Female rats were subjected to left coronary artery ligation followed by reperfusion and, 1weeks after MI, 4 different donor derived UCMSCs (M01, M02, M03, M04) were randomly transplanted into peri-infarct area (each n=5, 1X105). Eight weeks after ligation, all rats were sacrificed after echocardiographic evaluation. We evaluated the differentiation capacity of UCMSCs to cardiac phenotype by real time PCR, and paracrine function by ELISA in vitro. RESULTS Eight weeks after transplantation, 4 UCMSCs showed variable outcomes. Among 4 UCMSCs, M02 showed the best efficacy in improving LV systolic function, reducing infarct area, and preserving wall thickness. M02 showed enhanced cardiac specific gene expression under differentiation condition, and higher VEGF excretion compared to others. However, the engraftment efficacy of M02 was not higher than other donors. CONCLUSIONS There are differences in the efficacy of stem cell transplantation among UCMSCs derived from different donors. UCMSCs with better outcomes showed better cardiac commitment potential and paracrine capacity than other groups. Both differentiation potential and paracrine capacity of UCMSCs are important in cardiac regeneration.