Background: Simvastatin is a powerful drug that has cholesterol concentration lowering impact. But it can cause skeletal muscles complaints that vary from mild myalgia to deadly rhabdomyolysis. The safety of statins on skeletal muscles including diaphragm as a respiratory muscle remains questionable. Coenzyme Q10 (CoQ10) is a chemical substance that is naturally present in most living cells. It serves as mitochondrial respiratory chain electron carrier. Objective: The current study set out to assess the possible protective impact of exogenous CoQ10 administration on the potential histological alterations in the rat gastrocnemius and diaphragmatic muscles induced by simvastatin. Materials and Methods: Forty mature male rats were split equally into four groups; control group, CoQ10 treated group, Simvastatin-treated rats, and Simvastatin accompanied with CoQ10 for a period of 4 weeks. At end of experiment rat animals were slaughtered, serum creatine kinase (CK) concentration was measured. Right gastrocnemius and diaphragmatic muscles samples were excised to be prepared for light and electron microscopic study. Results: Simvastatin treated rats showed significant rise in CK concentration and histopathological alterations, in the form of loss of transverse striations, separation of myofibril, damaged mitochondria and enlarged sarcoplasmic reticulum. CoQ10 co- administration could mitigate simvastatin-induced histological alterations and restore the muscle fiber architecture due to its anti-fibrotic and anti-apoptotic impacts. Conclusion: Exogenous CoQ10 administration mitigated degenerative alterations in both skeletal and diaphragmatic muscles triggered by simvastatin administration.