Background: In the present study, we tested the hypothesis that carnitine supplementation counteracts obesityinducedmuscle fiber transition from type I to type II.Methods: 24 obese Zucker rats were randomly divided into two groups of 12 rats each (obese control, obesecarnitine) and 12 lean Zucker rats were selected for lean control group. A ... control diet was given to both controlgroups and a carnitine supplemented diet (3 g/kg diet) was given to obese carnitine group for 4 wk. Componentsof the muscle fiber transformation in skeletal muscle were examined.Results: The plasma level of carnitine were lower in the obese control group compared to the lean control groupand higher in the obese carnitine group than in the other groups (P < 0.05). Plasma concentrations of triglyceridesand non-esterified fatty acids were increased in obese animals compared to lean animals and the obese carnitinegroup had lower level compared to the obese control group (P < 0.05). The obese carnitine group had an increasednumber of type I muscle fibers and higher mRNA levels of type I fiber-specific myosin heavy chain, regulators ofmuscle fiber transition and of genes involved in carnitine uptake, fatty acid transport, β-oxidation, angiogenesis,tricarboxylic acid cycle and thermo genesis in M. rectus femoris compared to the other groups (P < 0.05).Conclusion: The results demonstrate that carnitine supplementation to obese Zucker a rat counteracts the obesityinducedmuscle fiber transition and restores the muscle oxidative metabolic phenotype. Carnitine supplementationis supposed to be beneficial for the treatment of elevated levels of plasma lipids during obesity or diabetes.