The risk for cardiovascular disease is significantly high in diabetes mellitus. Experimental evidence suggests that oxidative stress plays a dominant role in the pathogenesis of diabetes mellitus. Carvedilol, a non-selective beta-adrenoceptor and selective alpha1-adrenoceptor blocker, also has antioxidant and free radical scavenger properties. In the present study the effect of carvedilol on the antioxidative status of cardiac tissue was investigated in streptozotocin (STZ)-induced early diabetic rats. The subjects were randomly divided into age-matched rats, STZ-induced untreated diabetic rats, small and large dosage (1mg/kg/d or 10mg/kg/d) carvedilol-administrated diabetic rats. After 5 weeks, hemodynamic parameters, echocardiography characteristics and the levels of malondialdehyde (MDA), the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) in the cardiac tissues of all groups were meassured. Diabetic rats had lower ejection fraction, fractional shortening, and higher systolic pressure, diastolic pressure and developed pressure. These parameters were improved by administration of carvedilol. Diabetic rats showed elevated MDA level and CAT activity, but lower activities of SOD and GSH-Px. Carvedilol treatment increased activities of SOD and GSH-Px in diabetic rats. These results indicate that carvedilol improves cardiac function via its antioxidant property in diabetic rats.