Objective:To study the effects of catalpol on myocardial hypertrophy induced by isoproterenol (ISO) in mice. Methods Mice were randomly divided into four groups:normal group, model group, metoprolol(60 μg/g)group and catalpol(90 μg/g) group. Except the normal group,myocardial hypertrophy model was established by subcutaneous injection with isoproterenol at the dose of 2 μg/g for consecutive 7 days in mice that in the other groups. After drug intervention for 7 days,the heart weight index (HWI) and left ventricular weight index (LVWI) were determined. The activities of total superoxide dismutase (T-SOD) and the levels of glutathione (GSH) and malondialdehyde (MDA) in myocardial tissue were measured by hydroxylamine method,DTNB method and TBA method,respectively. The contents of cyclic adenosine monophosphate(cAMP) and angiotensin II (AngII) in myocardium were detected by ELISA.  Results: Compared with the normal control group, the HWI and LVWI were increased in the model mice of myocardial hypertrophy induced by ISO,and the contents of MDA,cAMP and AngII were increased and the GSH level was decreased(P<0.05,P<0.01). Catalpol treatment could significantly reduce the cardiac weight indexes and decrease the contents of MDA,cAMP and AngII in myocardium(P<0.05,P<0.01).  Conclusion: Catalpol has the effects of inhibiting myocardial hypertrophy in experimental animals,which are associated with the elimination of free radicals and inhibition of the over excitation of neuroendocrine system.