Background: Nonalcoholic fatty liver disease (NAFLD) is a disease gaining increasing interest worldwide. It ranges from simple nonalcoholic steatosis to nonalcoholic steatohepatitis (NASH), which is characterized by steatosis, inflammation and fibrosis, and may lead to liver cirrhosis and hepatocellular carcinoma. Objectives: To study the role of activin A, a member of the transforming growth factor (TGF) superfamily, in  diagnosis and evaluation of non-alcoholic fatty liver disease (NAFLD). Patients and Methods: This study is a comparative case-control study. This study was carried out at Outpatient Clinics of Internal Medicine Department of Ain Shams University.The study included 90 patients that were divided into 3 groups. Group < strong> 1 thatincluded 35 patients with NAS (steatosis) with exclusion criteria of intake of hepatotoxic drugs, group < strong> 2 that included 35 patients with fatty liver and elevated liver enzymes (NASH) and group < strong> 3 that included 20 patients as a control group. Results: There was a high statistical significant difference between the studied groups as regards ALT, AST, total and direct bilirubin, plts count, activin A, and Albumin. There was a high statistical significant difference between the studied groups as regards APRI score and FIB-4. There was high correlation between activin A and BMI, APRI score, FIB-4 and liver size with high significance (p < 0.001). Using activin A, it was shown that above 858.5, it can discriminate between NAFLD and non-NAFLD with level of sensitivity 100% and specificity 100%. Conclusion: Serum activin A showed a trend towards progressive level increase from controls, to steatosis and NASH patients.