Background: Non-alcoholic fatty liver disease (NAFLD) is a worldwide public health problem. It ranges from simple steatosis to steatohepatitis, liver cirrhosis and hepatocellular carcinoma (HCC). Ultrasonography is a noninvasive tool to examine the liver parenchyma. The aim of the current study is to evaluate the accuracy of ultrasonography in combination with fibroblast growth factor 21 (FGF21) in early detection and diagnosis of NAFLD, especially early stages (mild NAFLD). Patients and methods: A total of 340 eligible obese subjects were included in the study. They performed ultrasonographic examination with serum levels of FGF21 together with fasting blood glucose, insulin, glycated hemoglobin, total lipid profile, liver function tests and HOMA-IR. Results: There were significant differences in ultrasonographic findings and FGF21 serum levels between NAFLD group and non-NAFLD group. Roc curve showed a significant area under curve with a significant cutoff for FGF21 serum levels (>160 pg/mL) and intrahepatic triglyceride content (IHTC) (>5.79%). The sensitivity was 83.3% for FGF21 serum levels and 87.8% for IHTC and the specificity was 80% for FGF21 serum levels and 85% for IHTC. After combination of both FGF21 serum levels and IHTC, the sensitivity increased to 88.3% and the specificity was 80%. Conclusion: The combined use of ultrasonography and serum FGF21 has a higher sensitivity in the early diagnosis of NAFLD compared to either method alone.