INTRODUCTION: Nonalcoholic fatty liver disease (NAFLD) is characterized by high intrahepatic triglyceride level. It is associated with an increased prevalence of cardiovascular disease, independently of underlying cardiometabolic risk factors. Metformin is used as a pharmacological treatment; the adherence is low because of the presence of adverse effects. Aerobic exercise could be an alternative therapy, but its effectiveness compared with metformin has not been established in the treatment of NAFLD. The aim of this study was to establish the effectiveness of aerobic exercise and its influence in reducing cardiovascular risk in overweight or obese women with NAFLD. MATERIAL AND METHODS: Sedentary women 25-60 years old with body mass index (BMI) > 24.9 kg/m2 and liver fat content < 50 HU, were randomly divided into two parallel groups: exercise group (EG) or metformin group (MG). The EG performed an aerobic exercise program of 60 min/5 days/ week at 60-85% of heart rate reserve; the MG took 1 g/day of metformin each morning. The duration of the intervention was 12 weeks. The liver fat content, metabolic and cardiorespiratory- fitness parameters were evaluated at the beginning and end of the program. The study complied with the Helsinki ethics codes for human research. RESULTS: The study included a sample of 16 women, with 8 per group. The treatments modified the liver fat content by 14.6% (CI95% 0.92, 28.36) and 10.37% (CI95% -1.74, 22.48) for the EG and MG, respectively. In the EG, the insulin levels and HOMA-IR decreased (P < 0.05), and the cardiovascular fitness improved. CONCLUSIONS: An aerobic exercise program of 12 weeks with a volume training of 300 min/week and a moderate to vigorous intensity (60-85% VO2peak) modified the liver fat content and improved cardiovascular risk factors during the intervention. Exercise contributed to a holistic approach by modifying a number of the components of metabolic syndrome, cardiorespiratory-fitness, and cardiovascular risk.