Introduction: Metabolic disorders such as dyslipidemia and insulin resistance are associated with progression of non alcoholic fatty liver disease (NAFLD) and can lead to cardiovascular problems, the most common cause of death in these patients. The amount and composition of dietary fat are influential factors for blood lipid and glucose levels. The aim of this study was to assess the effects of virgin olive oil on serum lipid and glucose levels in the NAFLD patients on weight loss diets. Materials and Methods: This 12 week-clinical trial was carried out on 50 patients with non-alcoholic fatty liver). Subjects were randomly assigned into groups A (receiving the equivalent of 20% of total daily energy requirement from olive oil) or B (receiving their normal consumption of oil. At the beginning and end of the study, dietary intakes, anthropometric parameters, fasting plasma glucose and lipid levels were measured. Results: At the end of the study, as compared to commonly used oil, olive oil resulted in significant reductions of serum  triglycerides (P<0.05), and TG/HDL-C ratio [identified as an atherogenic index and a powerful predictor of cardiovascular disease risk] (P<0.05). Conclusions: Consuming a diet rich in virgin olive oil along with a slight weight loss in NAFLD patients, can be effective in the treatment and prevention of the consequences of cardiovascular complications of this disease.