Objective To observe the effect of endurance training on Mfn2 protein expression and mitochondrial function, so as to study the mitochondrial mechanism that endurance training elevated aerobic capacity in skeletal muscles of rats.Methods Twenty male wistar rats were randomly divided into control group (CN) and endurance training group (ET).Rats in ET swam 12 weeks while rats in CN feeded normally.After 12 weeks,the rats were anesthetized, then the gastrocnemius muscle mitochondria were rapidly extracted with differential centrifugation and measured MDA, MnSOD, respiration function, the expression of Mfn2 mRNA and protein.Results Comparing with NC group, in ET group, the activity of MnSOD increased significantly (P<0.01), while the MDA content reduced (P<0.05).The state 3 respiration and Mfn2 protein expression increased (P<0.05), and the respiration control ratio and Mfn2 gene expression increased obviously (P<0.01).While the state 4 respiration did not change.Conclusion 12-week endurance training markedly increased the expression of mitochondrial Mfn2 mRNA and protein in the skeletal muscles, which seems to be one of the factors for elevating aerobic capacity for skeletal muscles.