Abstract: Objective To investigate the effective of S-adenosyl-L-methionine (SAMe) on skeletal muscle mitochondrial DNA density and insulin sensitivity in Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Methods SAMe (15 mg /kg?d ) or placebo was administered intraperitoneally for 6-week-old OLETF rats. Food intake, body weight and skeletal muscle mitochondrial DNA density at different age were determined. Insulin sensitivity was evaluated by euglycemic-hyperinsulinemic clamp test. Results SAMe treatment significantly inhibited food intake and reduced body weight gain as well as increased skeletal muscle mitochondrial DNA density and whole body insulin sensitivity in OLETF rats compared with their controls. Furthermore, skeletal muscle mitochondrial DNA density correlated with insulin body weight (?=0.696. p<0.05). Conclusion SAMe treatment increased mitochondrial DNA density in the skeletal muscle , prevented body weight gain, and improved whole body insulin sensitivity in OLETF rats.