Introduction: One of the main mechanisms by which diabetic complications occur is an alteration of the structure and function of proteins due to hyperglycemia. Aspirin (ASA) affects cellular pathways through different mechanisms, including glycation inhibition and antioxidant activity. The aim of the present study, as a follow up to our previous one, is to investigate the effect of long-term, high-dose ASA therapy on mitochondrial respiratory chain complexes in the kidneys and brain of streptozotocin-induced diabetic rats. Its effect on liver toxicity of the rats was also investigated. Materials and Methods: High dose of ASA (100 mg/kg in drinking water) was administered to streptozotocin-induced diabetic rats during the twelve-week study period. After that, the rats were sacrificed under anesthesia and the tissues were retained -80 °C. Then the activity of respiratory chain complexes and the mentioned enzyme were measured in the brain, kidney, liver and serum of rats. Results: Treatment of diabetic rats with ASA could significantly compensate for the decreased activity of complex III respiratory chain in the kidneys. In addition, the activity of the liver enzymes (ALT, AST, ALP and LDH) in the serum of diabetic rats was significantly reduced by administration of ASA. However, there were no other significant functional changes observed in the kidney and brain respiratory chains complexes and the mentioned enzymes in liver. Conclusion: In conclusion, ASA therapy has a beneficial effect on the mitochondrial complexes and some serum enzymes in diabetic rats.