Backgraound Fractional flow reserve (FFR) is an important predictor of clinical outcomes after stent implantation. However, the clinical meaning of a trans-stent FFR gradient after stenting with a drug-eluting stent (DES) has not been adequately estimated. We evaluated the value and meaning of a FFR gradient across the stent for assessing the post-stent procedural results by comparison with intravascular ultrasound (IVUS) findings. Methods Eighty-six de novo intermediate coronary lesions (71, LAD; 9, RCA; 6, LCX) of 82 patients were treated with a DES (50, sirolimus-eluting stent; 31, everolimus-eluting stent; 5, zotarolimus-eluting stent). After angiographically successful stent implantation, coronary pressure and FFR were measured using the pull-back method under the continuous adenosine infusion. The 'trans-stent FFR gradient (��FFRstent)' was defined as gradient of FFR between the FFR just proximal to the stent and the FFR just distal to the stent. FFR gradient per 1mm of stent within the stented segment was defined as 'corrected ��FFRstent by stent length' (��FFRstent/length; ��FFRstent divided by whole stent length in the target lesion multiplied by 100). The angiographic and IVUS results of stenting were analyzed. Results FFR gradient across the stented segments existed in 81 lesions (94%) despite successful procedural results. Post-stent angiographic residual diameter stenosis was 8짹3%. Mean length and diameter of the stents were 33짹13mm and 3.3짹0.3mm. Minimal stent area (MSA), ��FFRstent and ��FFRstent/length were 6.8짹1.5mm², 0.033짹0.023 and 0.095짹0.048/mm, respectively. ��FFRstent correlated with stent length, but did not correlate with MSA (r=0.699, p<0.001; r=-0.177, p=0.102, respectively). However, ��FFRstent/length showed significant negative correlation with MSA (r=-0.305, p=0.005). Receiver operator characteristic analysis defined invariably a optimal ��FFRstent/length cut point at ��� 0.13/mm using the cut points of optimal MSA by IVUS; at this threshold, the sensitivity, specificity, and positive predictive value (PPV) and negative predictive value of ��FFRstent/length(��� 0.13/mm) were 86%, 67%, 97% and 27% for final MSA ���5mm²; 88%, 50%, 92% and 40% for final MSA ���5.5mm², respectively. Conclusions FFR gradient across the stent is frequently observed after stenting. Post-stent FFR gradient across the stented segment is related with stent length rather than with MSA. In contrast, corrected trans-stent FFR gradient by stent length could reflect MSA, thus ��FFRstent/length might be an useful index for assessing the procedural results of DES implantation itself with high PPV.