Background: Little is known regarding functional value of the fractional flow reserve (FFR) criteria to determine the successful results after percutaneous coronary intervention with drug eluting stent (DES) in diffuse long lesion of coronary artery. The present study compared the functional value of the FFR criteria to anatomic successful result criterias assessed by the intravascular ultrasound (IVUS) in diffuse long lesion of coronary artery with DES deployment. Methods: Fifty patients, 57 lesions with diffuse long coronary artery disease (>30 mm) were enrolled. After stent deployment with DES, we assessed the minimal lumen area (MLA), area stenosis (AS) by IVUS and FFR by intracoronary pressure wire. The FFR was defined as the ratio of mean distal coronary pressure of the lesion and the proximal coronary pressure during hyperemia induced by intracoronary bolus injection of adenosine (LCA: 48關g, RCA: 36關g). Results: The MLA after stent deployment showed a positive correlation with the FFR value (r=0.477, p<0.001) and AS revealed a significant inverse correlation with the value of FFR (r=-0.413, p=0.002). By receiver operating characteristics curve analysis, the best cutoff value of MLA for 0.94 of FFR value was 6.5 mm2 [area under the curve (AUC): 0.728, sensitivity: 66.7%, specificity: 76.2%]. The best cutoff value of FFR for 5.0 mm2 of MLA by IVUS was 0.91 (AUC: 0.734, sensitivity: 64.1%, specificity: 77.8%). Conclusion: Although the FFR value after DES deployment showed a significant correlation with the anatomic parameters obtained by IVUS, physiologic value of the FFR criteria for successful DES deployment was 0.91 and this is lower than previous results and further study about the optimal physiologic value of the FFR criteria might be required in diffuse long lesion after DES stent deployment.