Background: Ovarian masses are more common findings incidentally detected in symptomatic patients in every day work, to characterize them MRI is a modality of choice due to its high tissue contrast so MRI has high sensitivity, specificity and accuracy. Objectives: Assessment of role of MRI diffusion in differentiating of benign and malignant ovarian masses. Patients and method: Study was carried out on 60 female cases presented by ovarian masses referred from the OB/GYN out clinic and in patients between September 2019 and September 2020. The study was done in MRI unit, Diagnostic Radiology Department at Sohag Faculty of Medicine during the period from September 2019 to September 2020. For every patient a written consent was taken, patient's clinical data, pelvi-abdominal US, laboratory investigations and pelvis MRI were done. Results: 46 cases (76.7%) had benign ovarian lesions and 14 cases (23.3%) had malignant ovarian lesions. All the malignant cases (100%) show restriction at DWI while only 11 benign cases (23.9%) show restriction at DWI. The mean ADC was 1.76x10^-3 mm²/s, with a range from 0.5x10^-3 mm²/s to 3x10^-3 mm²/s (P value <0.001 (HS). The mean ADC was higher among benign cases (2.082x10^-3 mm²/s) compared to malignant ones (0.707x10^-3 mm²/s), ADC cut-off point is 0.895x10^-3 mm²/s, with a sensitivity of 89.1% and a specificity of 92.9% with P value <0.001. Conclusion: DWI and ADC value increases the accuracy of MRI to discriminate between benign and malignant lesions. Cut-off value was 0.89x10^-3 mm²/s to differentiate between benign and malignant ovarian masses.