Objective: To investigate the protective effects of Tangxinping Capsule, a compound traditional Chinese herbal medicine, on diabetic cardiomyopathy in rats.Methods: The model of diabetes mellitus was induced by streptozotocin (STZ) injection in rats. And the rats with diabetes mellitus were randomly divided into untreated group, metformin group, captopril group, and low-, medium- and high-dose Tangxinping group; the other ten normal rats were used as normal controls. After eight-week treatment, all rats were sacrificed to detect angiotensin Ⅱ (Ang Ⅱ) protein content and angiotensin Ⅱ type 1 receptor (AT1R) mRNA expression in myocardial tissues by radioimmunoassay and reverse transcription polymerase chain reaction (RT-PCR) respectively. The ultrastructural change in myocardial tissues was detected by transmission electron microscopy.Results: The results of radioimmunoassay and RT-PCR showed that the content of Ang Ⅱ protein and the expression of AT1R mRNA in myocardial tissue of the untreated group was significantly increased and more than those in normal control (P＜0.05, P＜0.01). Only the content of Ang Ⅱ and expression of AT1R mRNA in high-dose Tangxinping group and captopril group were significantly lower than those in the untreated group (P＜0.05, P＜0.01). The transmission electron microscopy showed that volume of mitochondrion in myocardial tissue in the untreated group was bigger than that in normal control group. Also the volume of mitochondrion was improved in 5 treated groups, but had no significant difference when compared with the untreated group.Conclusion: Tangxinping may adjust the disorder of renin-angiotensin system to protect myocardial tissue in rats with cardiomyopathy due to diabetes.