Objective：To investigate expressions of Th17 cell in rat model of pulmonary fibrosis（PF）. Methods：Totally 54 SD rats were randomly divided into 3 groups：control group（N group，n=18），PF model group（B group，n=18） and dexmethasone treated group（D group）. B and D groups were established by a single intra-tracheal injection of 5 mg/kg of bleomycin. N group received intra-tracheal instillation of saline instead. The next day D group was injected with dexamethasone（3 mg/kg） intraperitoneally every other day while N and B groups were injected with saline. Rats were sacrificed at the 7th，14 th，28th d after modeling in batch. Lung tissues were re－stored to analyze the pathological changes with HE staining and levels of hydroxyproline（HYP） in pulmonary tissues were determined. Proportion of CD4+IL-17+Th17 cells in the lung was evaluated by flow cytometry. Levels of serum interleukin-17（IL-17） were mea－sured by ELISA. Results：①In B group，biopsy of pulmonary tissues showed the dynamic process of change from pulmonary alveolitis to PF gradually. Levels of HYP in pulmonary tissues were higher in B group（the highest on the 28th d） than in N and D groups（P<0.05）. ②Th17 cell was lowly expressed in N group. Expressions of Th17 cell in pulmonary tissues and serum IL-17 were significant－ly higher in B and D groups than in N group at all time points（P<0.05），being most obviously at the 7th d. Conclusions：PF is developed by inflammatory damage and repair and has different pathological characteristics at different time points. Increased expres－sions of Th17 cell in pulmonary tissues of PF rats and serum IL-17 are associated with pulmonary inflammation and PF.