Objective To explore the effect and mechanism of aerobic exercise on islet β-cells in type 2 diabetic rats. Methods Thirty healthy SPF 8-week old Wistar rats were randomly divided into control group (C, n=10), diabetic control groups (DMC) and diabetic exercise (DME) groups, 10 rats in each group, among which 7 successful rat models were used in the experiment. The diabetic rat model was established by high fat and sugar diet and i.p. injection of streptozotocin in a dose of 50 mg/kg. The rats of group DME were forced to perform 20 m/min running for 30 min, once a day, 6 days in a week, for 8 weeks. Other rats were allowed free movement. At the end of experiment, serum glucose and insulin were measured and homeostasis model assessment (HOMA) was calculated, and pancreatic tissue samples were collected for histopathological examination. The morphology and structure of pancreatic islets were observed under a digital microscope, the perimeter and area of islets were analyzed by image analysis, and shape factor of islets was calculated. The insulin content, glucokinase and ultramicro-ATPase activity in the pancreatic homogenate were determined. Results In the DME group, the perimeter and area of islets were significantly higher than the DMC group (P<0.05), but still lower than the control group. The shape factor was significantly increased, the cell hypertrophy, vacuolization and nuclear pyknosis were markedly alleviated than those in the DMC group, the insulin content, glucokinase and the trace total ATP activity in the DME group were significantly higher than those in the DMC group (P<0.05), and the SF and HOMA were significantly changed. Conclusions Aerobic exercise can reduce the blood glucose level, improve the morphology of islets and β-cells in the type 2 diabetic rats. It may be due to increase of the activity of glucose kinase and ATP-synthase, and increased insulin sensitivity in the pancreas.