Background: Exercise and diet play a key role in management of type 2 diabetes.  Skeletal muscles secrete a variety of substances named myokines that are believed to mediate the beneficial effect of exercise. Irisin is a peptide secreted by skeletal muscles in response to exercise and also by adipocytes. So, it can be considered as myokine and adipokine. Irisin was reported to have an influence on glucose homeostasis and lipid metabolism.     Objective: To study the effect of chronic aerobic swimming exercise on serum irisin levels in type 2 diabetic rats, and clarify the possible association between these levels and some metabolic parameters. Material and Methods: The present study was carried out on a total number of 40 adult male albino rats divided into four equal groups: group I (standard diet sedentary group): animals were fed normal laboratory chow diet with no exercise training; group II (standard diet exercised group):  the rats were assigned  to chronic swimming exercise protocol of moderate intensity (1 h /day, 5 days/week for 8 weeks); group III (type 2 diabetic sedentary group): type 2 diabetes was induced using high-fat diet and a single intra-peritoneal injection of streptozotocin (35 mg/kg) then rats remained sedentary in their cages throughout the experimental period, and group IV (type 2 diabetic exercised group): the rats were trained by the same swimming exercise protocol after induction of type 2 diabetes. Results: Serum irisin level significantly increased in group II compared to group I. In group III, irisin level decreased significantly compared to group I and II. A significant increase in irisin level was found in group IV compared to group III but still significantly lower than group I and II. The results also revealed a non-significant change in blood glucose, serum insulin, HOMA-IR and HOMA-β between group I and II. Blood glucose level and HOMA-IR increased significantly in group III in comparison with group I and II. However, they showed a significant decrease in group IV versus group III, but these levels remain significantly higher than those of group I and II. A non-significant change was found in serum free T3 levels among groups, while a significant decrease in serum free T4 was noticed in group III compared to group I, II and IV. Conclusion: Type 2 diabetes was associated with a significant decrease in serum irisin level, while chronic swimming exercise training induced a significant increase in serum irisin in both healthy and type 2 diabetic rats.