Background:Wheezing is common in early childhood and remains an important health concem.The aim of this study was to assess the lung function of wheezing infants and to investigate the relationship between lung function and respiratory outcome.Methods:Infants ＜2 years of age with acute lower respiratory tract infection (ALRTI) who had undergone lung function tests were included in the study.They were assigned to wheeze or no wheeze group based on physical examination.Infants without any respiratory diseases were enrolled as controls.Lung function was measured during the acute phase and 3 months after ALRTI.One-year follow-up for infants with ALRTI was achieved.Results:A total of 252 infants with ALRTI who had acceptable data regarding tidal breathing were included in the final analysis.Compared with the control and the no wheeze groups,infants in the wheeze group had significantly decreased time to peak tidal expiratory flow as a percentage of total expiratory time (TPTEF/TE) (20.1 ± 6.4％ vs.34.4 ± 6.2％ and 26.4 ± 8.3％,respectively,P ＜ 0.0001) and significantly increased peak tidal expiratory flow (PTEF) (90.7 ± 26.3 ml/s vs.79.3 ± 18.4 ml/s and 86.1 ± 28.0 ml/s,respectively,P ＜ 0.01),sReffand Reff.The infants in the wheeze group still had lower TPTEF/TE and volume to peak tidal expiratory flow as a percentage of total expiratory volume (VPTEF/VE) than the no wheeze infants 3 months after the ALRTI.Moreover,there was a significant inverse relationship between TPTEF/TE,VPTEF/VE,and the recurrence of wheezing and pneumonia.Conclusions:Impaired lung function was present in wheezing infants with ALRTI and the deficits persisted.In addition,the lower level of TPTEF/TE and VPTEF/VE was a risk factor for poor respiratory outcome.