OBJECTIVE: To study the changes of pulmonary function in children with right lung middle lobe syndrome before and after treatment. METHODS: Thirty children with right lung middle lobe syndrome were classified into two age groups: ≤4 years old and >4 years old. Pulmonary function was tested by the 2600-type and the MIR-type pulmonary function spirometry in the ≤4 years and the >4 years age groups, respectively before and after treatment. Terminal flows/peak expiratory flow (25/PF) and the percentage of tidal volume to peak tidal expiratory flow (% V-PF) were measured in the <4 years age group. Forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and peak expiratory flow (PEF) were measured in the >4 years age group. RESULTS: The values of 25/PF and %V-PF in the ≤4 years age group were 0.42±0.08 and 0.28±0.03, respectively before treatment. The values were improved after treatment (0.58±0.12 and 0.39±0.06 respectively) (P<0.05). The values of FVC, FEV1 and PEF were 1.75±0.32, 1.36±0.52 and 2.56±0.78, respectively in the >4 years age group before treatment. The values were also improved after treatment (2.37±0.78, 2.08±0.65 and 3.68±0.80 respectively) (P<0.05). CONCLUSIONS: There are significant differences in the pulmonary function before and after treatment in children with right lung middle lobe syndrome. The pulmonary function can return to normal after treatment.［Chin J Contemp Pediatr, 2009, 11 (8):669-671］