The aim of this study was to examine the clinical value of iFR for AS patients. Functional evaluation of coronary stenosis in patients with aortic valve stenosis (AS) is challenging because the stress-induced test is often thought to be a contraindication. AS patients have a unique coronary flow pattern dependent on the diastolic phase. The instantaneous wave-free ratio (iFR) is a vasodilator-free, invasive pressure wire index of the functional severity of coronary stenosis and is calculated under resting conditions. And iFR calculated during a specific period of diastole may have the potential benefit to assess the functional severity of coronary stenosis in AS patients. We examined 158 consecutive patients (217 stenoses) whose iFR and fractional flow reserve (FFR) were measured simultaneously. Among the 158 patients, AS was observed in 13 (8.2%). The iFR showed good correlation with FFR in AS patients. The best cut-off value of iFR for the receiver-operator curve analysis to predict FFR of 0.8 was 0.9 for non-AS patients. However, it was 0.73 for AS patients. The present study demonstrated good correlation between iFR and FFR for AS patients. Vasodilator-free assessment using iFR may provide potential benefits when evaluating coronary stenosis in patients with AS. In AS patients, the best cut-off of iFR value predicting FFR value of 0.8 was lower than 0.9 that is the standard predictive value of iFR.