Objective To investigate the expressions of transforming growth factor-β1 ( TGF-β1), Clara cell secretory protein 16 (CC16), and type Ⅱ alveolar cell surface antigen 6 (Krebs Yon Denlungen-6; KL-6) in the lung tissue of bronchopulmonary dysplasia (BPD)-model rats and the relationship between the expressions of these proteins and lung cell apoptosis. Methods Newborn Sprague-Dawley rats were randomly divided into the control and model groups according to the random number table method . Rats in the model group were continuously exposed to 80% ~ 85% oxygen to construct the BPD model, and rats in the control group were always exposed to regular air. At 7, 14, and 21 days ( i.e., the 7 d model, 14 d model, and 21 d model groups), eight newborn rats were randomly selected and euthanized, and 5 mL of serum was retained. Hematoxylin and eosin staining was used to observe the lung histopathological changes in each group, and the radial alveolar count (RAC) and mean alveolar intercept were analyzed. TUNEL staining was used to detect apoptosis in the lung tissues of each group. Enzyme-linked immunosorbent assays were used to detect the TGF-β1, CC16 and KL-6 serum levels of newborn rats in each group. Western blot was used to detect the TGF-β1, CC16 and KL-6 expression levels in the lung tissue of each group. The relationships between the TGF-β1, CC16 and KL-6 expressions and the apoptosis rates in the lung tissue were analyzed. Results Compared with that of the normal group, the BPD injury to the lung tissue in the model group increased as the 80% ~ 85% oxygen exposure was prolonged. The serum levels of RAC and CC16 and the CC16 expression in the lung tissue were significantly reduced. At the serum level, the TGF-β1 and KL-6 expressions in the lung tissue were increased significantly (P<0. 05). Correlation analysis showed that the TGF-β1 and KL- 6 expressions in the lung tissue of the neonatal rats in the model group were positively correlated with the apoptosis rate in the lung tissue (r= 0. 977, 0. 970, P= 0. 000), and CC16 expression was correlated with apoptosis. The mortality rate showed a negative correlation ( r= - 0. 982, P= 0. 000). Conclusions TGF-β1, CC16, and KL-6 expression in lung tissue was closely correlated with apoptosis in the lung tissues of BPD-model rats.