OBJECTIVE：To preliminarily investigate the improveme nt effects and mechanism of Mongolian medicine Saorilao-4 decoction on specific pulmonary fibrosis model rats. METHODS ：Male SD rats were randomly divided into normal control group ，model group ，positive control group （pirfenidone，0.163 g/kg）and Saorilao- 4 decoction low ，medium and high dose groups （0.899，1.798，3.596 g/kg），8 rats in each group. Except for normal control group ，other groups were given 6 mg/mL bleomycin intratracheally at 5 mg/kg once to induce the specific pulmonary fibrosis model. From the first day after modeling ， normal control group and model group were given normal saline intragastrically ，other groups were given corresponding drugs intragastrically，once a day ，10 mL/kg，for 4 weeks. During the experimental period ，the general condition of the rats in each group was observed and the body mass was weighed. Twenty-four h after last medication ，the appearance morphology of rat l ung in each group were observed. The morphological characteristics of lung tissues were observed by HE and Masson staining. ELISA was adopted to determine the activity of SOD and the content of MDA in serum ，the contents of hydroxyproline （HYP），IL-1β，IL-6，hyaluronidase（HA），laminin（LN）precollagen type Ⅲ（PC-Ⅲ）and collagen type Ⅳ（Col-Ⅳ）in lung tissue. RT-PCR was used to determine the mRNA 发。E-mail：bwf007007@sina.com expression of TGF-β 1，Smad3 and Smad 7 in lung tissue. RESULTS：Compared with model group ，the activity ，hair and diet of the rats in each dose group of Saorilao- 4 decoction and positive control group were significant ly improved ，and the body mass after the last administration was significantly increased ； the pathological change of lung and pulmonary fibrosis were significantly improved ，and the activity of SOD in serum was increased significantly. Serum content of MDA （except for Saorilao- 4 decoction medium dose group ），the contents of HYP （except for Saorilao- 4 decoction high dose group ），IL-1β，IL-6，HA，LN，PC-Ⅲ，Col-Ⅳ（except for Saorilao- 4 decoction high dose group）as well as mRNA expression of TGF-β1 and Smad 3 in lung tissue were significantly decreased ；mRNA expression of Smad 7 was significantly increased （P＜0.05 or P＜0.01）. CONCLUSIONS ：Saorilao-4 decoction can significantly improve the lung pathological changes ，delay and reverse the progression of pulmonary fibrosis in specific pulmonary fibrosis model rats ，the mechanism of which may be related to the inhibition of inflammatory response ， improvement of lipid peroxidation ， down-regulation of TGF-β1 and Smad 3 mRNA expression ，and up-regulation of Smad 7 mRNA expression.