Abstract: Objective　To study clinical significance of single tidal breathing testing in bronchiolitis. Methods Infants with bronchiolitis at first wheezing (bronchiolitis group, n=756), and 115 infants with bronchopneumonia (bronchopneumonia group) hospitalized were enrolled. Tidal breathing parameters were analyzed in two groups. Bronchiolitis group was divided according to percentiles of the fraction of exhaled time at peak tidal expiratory flow to total expiratory time (TPTEF/TE). The episodes of recurrent wheezing of infants below the 20th or above the 80th percentile of TPTEF/TE were followed up by phone calls within 1 year after discharge from the hospital. Results There were significant differences in TPTEF/TE, VPEF/VE, Ti, Ti/Te, TEF75 and TEF50 between bronchiolitis group and bronchopneumonia group. The recurrent wheezing rate of infants with bronchiolitis below the 20th percentile of TPTEF/TE was significantly higher than that above the 80th percentile of TPTEF/TE (37.5% vs 11.3%). Conclusions There is the greater possibility of recurrent wheezing in the infants with the more serious airway obstruction reflected by single tidal breathing testing in bronchiolitis.