Objective To observe the effects of combined antioxidant micronutrients (CAM) on myocardium ultrastructure of type one diabetic mellitus (T1DM) mice. Method T1DM mice model was made by injection of multiple low dosages of streptozotocin (MLDS). The supplementation of CAM was designed CAM4 and CAM7 two groups. The ultrastructure of myocardium in T1DM mice was observed by electron microscope and measured by computer image analysis method. Results The blood glucose level of mice in CAM4 and CAM7 groups was significantly decreased and the depth of microvascular basement membrane was smaller as compared with that of T1DM model group. The structure of mitochondria and myofilament was improved and the swelling of mitochondria was lightened in both CAM4 and CAM7 group. Conclusion Combined antioxidant micronutrients may protect ultrastructure of myocardium in T1DM mice.