Objective：To explore the effect on pulmonary fibrosis，cell apoptosis and expression of Fas/FasL in lung by blocking IL-17 activity in mice induced by bleomycin(BLM). Methods：Eighty C57BL/6 mice were randomly divided into the following 4 groups：sham group(SG)，BLM group(BG)，neutralizing antibody group(NG) and isotype-matched control antibody group(IG)，respectively. Three groups were received a single intratracheal instillation of 5 mg/(kg body weight) of BLM to induce pulmonary fibrosis，while SGs was administrated the equvalent sterile saline. NG and IG were injected through caudal vein with neutralizing rat antimouse IL-17 mAb，or control rat IgG every 3 days starting on day 1 before making model，SG and BG were received equvalent PBS alone. All mice were sacrificed after 28 days. Lung tissues were removed and used to evaluate the extent of pulmonary fibrosis by Masson staining and hydroxyproline contents measurement. Cell apoptotic rate and the expression of Fas/FasL in mice were detected through Flow cytometry and immunohistochemical method. Results：Compared with BG and IG，the pulmonary fibrosis degree of NG was decreased remarkably(P＜0.01). Hydroxyproline contents was reduced obviously(P＜0.01). Apoptotic rate and expressions of Fas/FasL were decreased significantly(P＜0.01). Conclusion：Pulmonary fibrosis was improved significantly after the endogenous IL-17 activity blocked，meanwhile，apoptosis and the expressions of Fas/FasL were both decreased. These data showed that antimouse IL-17 mAb ameliorate the pulmonary fibrosis induced by BLM and it is related to Fas/FasL apoptotic pathways.