Abstract: Objective To investigate the effects and mechanism of leucine on nonalcoholic fatty liver disease(NAFLD) induced by high fat diet in rats.Methods Forty male Sprague-Dawley rats fed with 60% high fat diet were randomly divided into 4 groups:one high-fat diet group and three leucine groups with 1.5%,3%,and 4.5% leucine in the high-fat diet,respectively.At the end of 16 weeks' treatment,the serum alanine aminotransferase(ALT),aspartate transferase(AST),total cholesterol(TC),triglycerides(TG),low density lipoprotein cholesterol(LDL-C),high density lipoprotein cholesterol(HDL-C),liver hepatic total anti-oxidation capacity(T-AOC),total superoxide dismutase(T-SOD),reduced glutathione hormone(GSH-Px),and malondialdehyde(MDA) were measured.The pathological changes in the livers of the rats were also observed.Results Obvious fatty degeneration of the livers was observed in the rats of the high-fat diet group.Serum levels of ALT,AST in leucine groups were signi-ficantly lower than those of the high-fat diet group.The serum TC in 3.0% and 4.5% leucine groups were 2.35±0.30 and 2.60±0.57 mmol/L,which were signifi-cantly lower than those of the high-fat diet group.Compared to those of the high-fat diet group,significantly higher T-SOD(285.99±53.53,272.47±65.02 vs.208.24±63.57 U/mg.prot,P<0.01) and GSH-PX(506.02±140.34,483.44±131.44 vs.209.50±80.38 U/mg.prot,P<0.01) were detected in the liver of the rats of 1.5% and 3.0% leucine groups,but significantly lower MDA(0.47±0.14 vs.1.04±0.43 nmol/mg.prot,P<0.01) was detected in 4.5% leucine group.Conclusion Leucine improves NAFLD induced by high fat diet in rats and the effect is related to improving lipid metabolism and antioxidant capacity.