Background: Optimal intravascular ultrasound (IVUS) criteria for the functional significance of patients with intermediate coronary stenoses have been introduced, but not fully evaluated yet. We would like to make a comparison between the parameters of IVUS criteria and fractional flow reserve (FFR). Methods: IVUS and FFR measurement were performed in 359 intermediate lesions located at the proximal and middle of major epicardial coronary arteries. The functionally significant stenosis was defined as FFR < 0.8. Significant lesion assessment by IVUS was defined as minimal lumen area (MLA) < 4.0mm2 and plaque burden (PB) > 70%. Results: Functional significance of intermediate lesion was more related to MLA than %PB. Although there was a significant correlation between optimal IVUS criteria and FFR, 58.6% of significant stenotic lesion by IVUS was still functional patent by FFR. Comparison of IVUS criteria and functional significance is shown in figure. Conclusions: When the FFR are used to determine the functional significance of IVUS criteria in patients with intermediate stenosis, large portion of significant stenotic lesions by IVUS criteria are still functionally insignificant.