OBJECTIVE：To study the improvement effects of baicalein against myocardial ischemia/reperfusion（I/R）injury in rats. METHODS：I/R injury model was induced by Langendorff method. Isolated heart of 40 rats were randomly divided into normal group（continuous perfusion），model group（perfusion withdrawal 20 min）and baicalein high，medium and low concentration groups（K-H solution of baicalein 40，10 and 2.5 μmol/ml 10 min before perfusion withdrawal）. The myocardial infarction rate， the activity of creatine kinase（CK）and lactate dehydrogenase（LDH）in coronary effluent liquid，SOD activity and MDA content， GSH/GSSG and apoptosis rate of cardiac muscle cell in myocardial tissue were detected. RESULTS：Compared with normal group， the myocardial infarction rate，apoptosis rate of cardiac muscle cell，the activities of CK and LDH and the content of MDA in myocardial tissue were increased in model group，while SOD activity and GSH/GSSG of myocardial tissue decreased（P＜0.01）. Compared with model group，the isolated myocardial infarction rate and the activities of CK and LDH in baicalein low and medium concentration groups decreased，while SOD activity increased（P＜0.05 or P＜0.01）；apoptosis rate of cardiac muscle cell and the content MDA of myocardial tissue decreased significantly in medium concentration group，while GSH/GSSG increased（P＜0.05 or P＜0.01）；those indicators had no significant change in high concentration group（P＞0.05）. CONCLUSIONS：Baicalein has certain improvement effect on myocardial I/R injury in rats，and its mechanism may be associated with antioxidant and anti-apoptosis effect of baicalein.