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Background: Despite the positive effects of high-intensity training on weight management and health-related outcomes, it is postulated that high-intensity training may also induce oxidative stress, increasing hepatic damage.Aim: The aim of this study was to compare the effects of low versus high-intensity training on biomarkers related to non-alcoholic fatty liver disease (NAFLD) in adolescents with obesity.Methods: For this study 107 adolescents (15 ± 1 years) with obesity (BMI = 34.7 ± 4.1 kg/m2) were randomized into High-Intensity Training (HIT, n= 31), Low-Intensity Training (LIT, n= 31) or Control Group (CG, n= 45). Adolescents from HIT and LIT received nutritional, psychological and clinical counseling. Blood lipids, Castelli risk index, glucose, insulin and hepatic enzymes were measured at baseline and after 12 weeks.Results: Castelli risk index 1 was reduced in all groups (p< 0.001) with moderate effect size (d) for HIT (d= 0.62) and LIT (d= 0.66). Castelli risk index 2 also decreased (p< 0.001 for all groups; HIT d= 0.65; LIT d= 0.79). High-density lipoprotein increased in all groups (d= 0.25 and d= 0.18 in HIT and LIT), while alanine aminotransferase tended to reduce (p= 0.062) in HIT (d= 0.34) and LIT (d= 0.73) and aspartate aminotransferase decreased (p= 0.024) in both HIT (d= 0.24) and LIT (d= 0.45). There were no changes in glucose, insulin and insulin resistance.Conclusion: Both high and low-intensity training improved biomarkers related to NAFLD. Thus, high-intensity training can be a safe and effective alternative to prevent and treat NAFLD in adolescents with obesity.