AIM: To investigate if conjugated linoleic acid supplementation (CLA) affects metabolic factors and oxidative stress in non-alcoholic fatty liver disease (NAFLD). METHODS: The study was a randomized, controlled clinical trial conducted in specialized and subspecialized clinics of Tabriz University of Medical Sciences from January 2014 to March 2015. 38 obese NAFLD patients were randomly allocated into either the intervention group, receiving three 1000 mg softgel of CLA with a weight loss diet and 400 IU vitamin E, or into the control group, receiving only weight loss diet and 400 IU vitamin E for eight weeks. Dietary data and physical activity, as well as anthropometric, body composition, metabolic factors, and oxidative stress were assessed at baseline and at the end of the study. RESULTS: Weight, body composition, and serum oxidative stress, insulin, and lipid profile significantly improved in both groups, while hemoglobin A1c (HbA1c) levels (P=0.004), total cholesterol to high density lipoprotein ratio (P=0.008), low density lipoprotein to high density lipoprotein ratio (LDL/HDL) (P=0.002), and alanine aminotransferase to aspartate aminotransferase (ALT/AST) ratio (P=0.025) significantly decreased in the intervention group. At the end of the study, fat mass (P=0.001), muscle mass (P=0.023), total body water (P=0.004), HbA1c (P<0.001), triglycerides (P=0.006), LDL/HDL ratio (P=0.027), and ALT/AST ratio (P=0.046) were significantly better in the CLA group than in the control group. CONCLUSION: CLA improved insulin resistance, lipid disturbances, oxidative stress, and liver function in NAFLD. Therefore, it could be considered as an effective complementary treatment in NAFLD.