Fraction flow reserve (FFR) is considered the gold standard for assessing intermediate coronary lesions. Retrospective data analyses showed variable relationship between intravascular ultrasound (IVUS) parameters and FFR results. This study aimed to determine the optimal minimum lumen area (MLA) by IVUS that correlates with FFR and to assess the correlation between two modalities in assessing intermediate coronary lesions. Methods: Fifty eight intermediate coronary lesions mainly located in proximal and mid segments of large main coronary vessels with reference vessel diameter (RVD) between 3-4mm were analyzed using both IVUS and FFR to assess the significance of coronary stenting and to determine the optimal IVUS-MLA that correlates with FFR value < 0.8. Results: IVUS-MLA ranged from 2.5 to 4.2 mm2 had a highly significant positive correlation with FFR value < 0.8 (p < 0.0001). Using the ROC curve analysis, IVUS-MLA < 3.9 mm2 (84.2% sensitivity, 80% specificity, area under curve (AUC) = 0.68) was the best threshold value for identifying FFR