Background: Nonalcoholic fatty liver disease (NAFLD) is one of the most important precursors of chronic liver disease all over the world. Doppler ultrasonography is an essential part of evaluating the vascular haemodynamic variation seen within NAFLD. Objective: Assessment of the role of Hepatic Artery Resistive Index (HARI) in NAFLD patient and the relation between HARI and grading of fatty liver by ultrasound. Patients and methods: One hundred Egyptian patients diagnosed to have NAFLD based on ultrasound abdomen 35, 35, and 30 patients in grade1, grade 2, and grade3 NAFLD, respectively and 20 healthy subjects as control group were subjected to hepatic artery Doppler study. The study was carried out in the Outpatient Clinic of Internal Medicine Department, Faculty of Medicine, Al-Azhar University, Assiut, Egypt. Results: Our study results showed high statistical significant difference (p-value < 0.001) between studied groups as regards hepatic artery resistance index. There was an inverse relationship between HARI and different grades of fatty liver in patients (p < 0.001). Hepatic artery resistance index (RI) decreased as the severity of diffuse fatty infiltration increases. Conclusion: Hepatic artery resistance index (RI) decreases as the severity of diffuse fatty infiltration increases.