OBJECTIVE To study the protective effects of mangiferin against oxidative stress injury of myocardial cells induced by hydrogen peroxide （H2O2）， and its effects on the expression of nuclear factor of activated T cell cytoplasmic 4（NFATc4）. METHODS H9c2 myocardial cells were cultured in vitro and divided into blank group， H2O2 group， and 50， 100， 150 μmol/L mangiferin groups. Mangiferin groups were treated with different concentrations of mangiferin for 12 h， and then were subjected to H2O2 （200 μmol/L） stimulation for 12 hours together with the H2O2 group； relative survival rate was detected in each group， and the levels of superoxide dismutase （SOD）， catalase （CAT） and malondialdehyde （MDA） in cell supernatant and reactive oxygen species （ROS） in H9c2 cells were measured. Meanwhile， the expressions of apoptosis-related proteins [B cell lymphoma 2 （Bcl- 2）， Bcl-2 associated X protein （Bax）， cleaved caspase-3] and nuclear protein NFATc4 were determined. Furthermore， the NFATc4 interference sequence was transfected， and the effects of NFATc4 on oxidant stress indexes and apoptosis-related proteins in H2O2- induced myocardial cells were investigated. RESULTS Compared with blank group， relative cell viability， the levels of SOD and CAT， relative expression of Bcl-2 were decreased significantly， while the levels of MDA and ROS， relative expressions of Bax， cleaved caspase-3 and nuclear protein NFATc4 were increased significantly （P＜0.05 or P＜0.01）. Compared with the H2O2 group， the above indexes of 100 and 150 μmol/L mangiferin groups were reversed significantly （P＜0.05）. After the transfection of the NFATc4 interference sequence， the expression of nuclear protein NFATc4 was down-regulated significantly； the levels of MDA and SOD， the protein expressions of Bax and cleaved caspase-3 were all decreased/down-regulated significantly， while the levels of SOD and CAT， and the protein expression of Bcl-2 were all increased/up-regulated significantly， compared with H2O2 group （P＜ 0.05）. CONCLUSIONS Mangiferin can relieve H2O2-induced oxidative stress of H9c2 cells， reduce the apoptosis and inhibit the nuclear translocation of NFATc4， thereby alleviating myocardial cell damage； reducing the nuclear level of NFATc4 protein is related to reducing H2O2-induced oxidative stress and cell apoptosis.