Diabetic cardiomyopathy (DCM) is diagnosed when patients with diabetes develop ventricular dysfunction but do not exhibit coronary atherosclerosis or hypertension. Cortex Mori (CM) Radicis,he epidermis of the root of Morus alba L, has been traditionally used for cough treatment in oriental medicine. In this study, we investigated the protection of myocardium by CM in streptozotocin (STZ)-induced diabetic rats and the underlying mechanisms. Diabetes was induced in rats by an injection of STZ at 25mg/kg. The animals were randomly divided into 4 groups: control, diabetes, diabetes with CM treatment, diabetes with CM preventative treatment. Pathological changes were examined by hematoxylin-eosin staining. Extracellular matrix content was assessed by Masson’s trichrome staining and Western blot. Endoplasmic reticulum (ER) stress-associated molecules and main components of the mitogen-activated protein kinase (MAPK) pathway were also measured by Western blot. Myocardial damages were induced by the injection of STZ as evidenced by abnormal blood glucose and pathological cardiac changes. Administration of CM markedly ameliorated myocardial damages such as cardiac hypertrophy and fibrosis. ER stress was down-regulated, and p38 and ERK were suppressed by CM. Thus, CM may have therapeutic potential in the treatment of DCM by attenuating ER stress and ERK and p38 MAPK activation.