Ischemia postconditioning (IpostC) is an effective way to alleviate ischemia and reperfusion injury; however, the protective effects seem to be impaired in candidates with diabetes mellitus. To gain deep insight into this phenomenon, we explored the role of DJ-1, a novel oncogene, that may exhibit powerful antioxidant capacity in postconditioning cardioprotection in a rat model of myocardial ischemia reperfusion injury. Compared with normal group, cardiac DJ-1 was downregulated in diabetes. Larger postischemic infarct size as well as exaggeration of oxidative stress was observed, while IpostC reversed the above changes in normal but not in diabetic rats. DJ-1 was increased after ischemia and postconditioning contributed to a further elevation; however, no alteration of DJ-1 was documented in all subgroups of diabetic rats. Alteration of the cardioprotective PI3K/Akt signaling proteins may be responsible for the ineffectiveness of postconditioning in diabetes. There is a positive correlation relationship between p-Akt and DJ-1 but a negative correlation between infarct size and DJ-1, which may partially explain the interaction of DJ-1 and IpostC cardioprotection. Our result indicates a beneficial role of DJ-1 in myocardial ischemia reperfusion. Downregulation of cardiac DJ-1 may be responsible for the compromised diabetic heart responsiveness to IpostC cardioprotection.