Background: When patients with chronic respiratory symptoms have a normal spirometry result, it is not always easy to consider bronchial asthma as the preferential diagnosis. Forced expiratory flow between 25% and 75% of vital capacity (FEF25~75%) is known as a useful diagnostic value of small airway diseases. However, it is not commonly used, because of its high individual variability. We evaluated the pattern of bronchodilator responsiveness (BDR) and the correlation between FEF25~75% and BDR in patients with suspicious asthma and normal spirometry. Methods: Among patients with suspicious bronchial asthma, 440 adult patients with a normal spirometry result (forced expiratory volume in one second [FEV1]/forced vital capacity [FVC] ≥70% & FEV1% predicted ≥80%) were enrolled. We divided this group into a positive BDR group (n=43) and negative BDR group (n=397), based on the result of BDR. A comparison was carried out of spirometric parameters with % change of FEV1 after bronchodilator (ΔFEV1%). Results: Among the 440 patients with normal spirometry, FEF25~75%% predicted were negatively correlated with ΔFEV1% (r=?0.22, p＜0.01), and BDR was positive in 43 patients (9.78%). The means of FEF25~75%% predicted were 64.0±14.5% in the BDR (＋) group and 72.9±20.8% in the BDR (?) group (p＜0.01). The negative correlation between FEF25~75%% predicted and ΔFEV1% was stronger in the BDR (＋) group (r=?0.38, p=0.01) than in the BDR (?) group (r=?0.17, p＜0.01). In the ROC curve analysis, FEF25~75% at 75% of predicted value had 88.3% sensitivity and 40.3% specificity for detecting a positive BDR. Conclusion: BDR (＋) was not rare in patients with suspicious asthma and normal spirometry. In these patients, FEF25~75%% predicted was well correlated with BDR.