Abstract: Objective To study the effects of hydrogen peroxide on DNA damage and apoptosis in myocardial H9c2 cells line.Methods H9c2 cells were exposed to different concentration of H₂O₂(50,100,200,400μmol/L)in different time(1,3,6,12,24h).The cell viability was measured by MTT assay.Apoptosis was determined by AO/EB double fluorescent staining assay.The single cell gel electrophoresis(SCGE)was used to study the DNA damage of H9c2 cells.Results The experimental results demonstrated that H₂O₂ could damage H9c2 cells in dose dependant and time dependant way(P <0.05),and induce apoptosis with obviously morpho logical changes in exposed groups(P<0.05),especially at 6h,100 μmol/L level of H₂O₂,compared with NC(P<0.01).H₂O₂ could cause DNA damage.The rate of DNA damage was increased with the increase of dosage(P<0.01).Conclusion H₂O₂ could cause oxidative injury and DNA damage in H9c2 cells.Apoptosis and necrosis are main outcomes depending on exposure dose and exposure time.