AIM: To investigate the effect of ecdysterone (EDS) on H9c2 cardiomyocytes after oxidative stress.METHODS:H9c2 cells were cultured in vitro and divided into control group, high dose (2 μmol/L) of EDS group, middle dose (1.5 μmol/L) of EDS group, low dose (1 μmol/L) of EDS group, and H2O2 group.H9c2 cardio-myocytes in H 2 O2 group and high , middle and low doses of EDS groups were exposed to H 2 O2 for 6 h to establish the model of oxidative stress.The viability of the H9c2 cells was detected by CCK-8 assay.The apoptosis of H9c2 cells was analyzed by flow cytometry.The levels of lactate dehydogenase (LDH) and creatine kinase-MB (CK-MB) in the culture medium, and the levels of superoxide dismutase (SOD) and malondialdehyde (MDA) in the H9c2 cells were measured by colorime-try.The generation of reactive oxygen species (ROS) and the mitochondrial membrane potential were evaluated by flow cy-tometry and confocal laser scanning microscopy .The protein levels of Bax , Bcl-2 and cleaved caspase-3 in the H9c2 cells were determined by Western blot .RESULTS:Ecdysterone at the selected concentrations had no effect on the viability of H9c2 cells.Compared with control group, the levels of LDH, CK-MB, ROS and MDA, and the apoptotic rates of the H9c2 cells were significantly increased after treated with H 2 O2 , but were decreased by EDS treatment in a dose-dependent man-ner.The levels of SOD and mitochondrial membrane potential of the H 9c2 cells in H2 O2 group were reduced significantly compared with control group , but high, middle and low doses of EDS treatments up-regulated the levels of SOD and mito-chondrial membrane potential in H 2 O2-treated H9c2 cells.The protein levels of Bax and cleaved caspase-3 in the H9c2 cells in H2 O2 group showed significant elevation in comparison with control group , and the protein expression of Bcl-2 de-clined in H2 O2 group compared with control group , but high, middle and low doses of ecdysterone treatments down-regula-ted the protein levels of Bax , cleaved caspase-3 and up-regulated the expression of Bcl-2 in H2 O2-treated H9c2 cells. CONCLUSION:Ecdysterone attenuates the effect of H 2O2-induced oxidative stress on H9c2 cardiomyocytes.The mecha-nism may be involved in scavenging oxidative stress products , increasing antioxidant enzyme activity and improving mito-chondrial function .