Aim To explore the expression of micorRNA-503 and its target genes,in process of diabetes mellitus induced impairment reparative angiogenesis after acute myocardial infarction. Methods GK rats and Wistar rats 30 each were made into the model of acute myocardial infarction by ligating the left anterior descending coronary artery. Capillary density around the region of infarction was detected by immunohistochemical staining with vWF,expression of micorRNA-503 was measured by qRT-PCR,and the protein expressions of cyclinE1 and cell division cycle 25A （CDC25A） were measured by Western blot. Analysis of cappilaries,micorRNA-503,cyclinE1 and CDC25A were made on days 0（pre-ligation）,3,7,14 and 28 days post-ligation. Results In each time point post-ligation,the capillary density around the region of infarction and expression of CDC25A decreased in GK rats compared with Wistar rats,the expression of micorRNA-503 increased significantly （P<0.05）. Decreased expression of cyclinE1 in GK rats was only observed on 14 and 28 days post-ligation （P<0.05）. Conclusion Our data suggest that micorRNA-503 contribute to diabetes mellitus induced impairment reparative angiogenesis after acute myocardial infarction,via down-regulation of CDC25A.