Objective:To observe protective action of Atenolol on hydrogen peroxide(H2O2) induced cardiomyocytes over-oxidation injury and investigate the mechanism. Methods:A model of cardiomyocytes injuried by H2O2 was established,and the protective effects of Atenolol on the injury was investigated. The morphology of cardiomyocytes and cardiomyocytes surviving fraction were measured. The activities of lactate dehydrogenase(LDH) and malondialdehyde(MDA) were also assayed. Results:Atenolol dose enhance cardiomyocytes surviving fraction(P < 0.05),and decrease the activities of LDH and MDA in the injuried myocytes(P < 0.05). Conclusion:Atenolol has the protective effects on cardiomyocytes injured by H2O2 through improving cell antioxidant ablility.