Abstract: Objective To study the value of small airway function for predicting airway hyper responsiveness. Methods One hundred and ninety-four patients with chronic cough who had suspected airway hyper responsiveness with normal ventilation function and bronchial dilation testing were enrolled in this study.Correlation between small airway function,airway reactivity and sensitivity was analyzed. Results The positive rate for bronchial challenge testing was 72.68% in these patients.The forced expiratory flow（FEF） rate was 25%,50%,and 75%,respectively.The maximal mid-expiratory flow（MMEF） rate was significantly lower in patients receiving positive challenge testing than in those receiving negative challenge testing（P＜0.01）.No significant difference was observed in vital capacity（VC）,forced VC（FVC）,forced expiratory volume 1（FEV1）,and peak expiratory flow（PEF）.The incidence of small airway dysfunction was 39.18%.The positive challenge testing rate was 92.11% in abnormal group and 60.17% in normal group（P＜0.05）.A significant difference was found in Rrs,Grs,Dmin,and PD35 but no significant difference was observed in SGrs between normal and abnormal small airway function groups.The small airway function was correlated with the airway reactivity and sensitivity（r=0.47）.Multiple regression analysis showed that the FEF was 25%,50% and 75%,respectively,while the coefficient for MMEF of PD35 and Dmin was 0.472 1 and 0.459 1,respectively（P＜0.05）.Logistic regression analysis displayed that the abnormal small airway function exerted a significant effect on the challenge testing（P=0.000 3,OR=6.19）. Conclusion Small airway function in patients receiving positive bronchial challenge testing is significantly different from that in those receiving negative bronchial challenge testing.Decreased small airway function is of a certain value for predicting the airway hyper responsiveness.