METHODS: We recruited 70 (discovery set) and 24 bronchiectasis patients (validation set), and 26 healthy subjects. The diagnostic value of small airway parameters was compared with the receiver operation characteristic curve. Chest high-resolution computed tomography (HRCT), IOS measurement, spirometry, and sputum culture were performed. Correlation between SAPs and clinical indices was determined, adjusting for age, sex, body-mass index and smoking history. Sensitivity analyses were repeated when excluding patients with BSI ≥9 or HRCT score ≥7.