Objective:To explore the mechanism of intervention effect of Dahuang Zhechong Wan on the formation stage of pulmonary fibrosis in rats.Method:The pulmonary fibrosis model was induced by bleomycin A 5（BLMA 5）.Rats in herbal groups were administrated with Dahuang Zhechong Wan（consisted of rhubarb and eu-polyphaga） from the day 14

and sacrificed on day 28.Then superoxide dismutase（SOD） activity and the contents of malondialdehyde（MDA）in serum and in bronchoalveolar lavage fluid（BALF） were determined and analyzed.Re-sult:The SOD activity in serum and BALF in model group were lower than those in control group.the MDA contents in serum and BALF in the model group were higher than those in the control group.SOD activity in Dahuang Zhe-chong Wan group were higher than those in the model group

MDA contents in Dahuang Zhechong Wan group were lower than those in the model group.Conclusion:Dahuang Zhechong Wan had the functions of restraining the de-cline of the SOD activity and the increase of MDA contents of the mode with pulmonary fibrosis and serum.The SOD activity and MDA contents of serum indirectly reflected the level of lipid peroxidation and antioxidation of the lung.