Objective:To observe the effect of Yiqiyangyin Decoction( YQYY) on bleomycin-induced rats pulmonary fibrosis and the expression of Smad2 and Smad7.Methods:Sixty male SD rats were randomly divided into normal group,model group,YQYY group,hormone group,YQYY plus hormone group.The rats in the normal group injected saline via the trachea,the rest rats injected ble-omycin(5 mg/kg).From the second day of injection,YQYY group were treated with YQYY decoction(1 ml/100 g);hormone group were given 35%Prednisone acetate solution(1 ml/100 g);YQYY plus hormone group were treated with the mixture of YQYY decoction and hormone (1 ml/100 g);normal group and model group were given equivalent saline.After twenty-eight days,all the rats were killed,the rat lung histopathology was examined with HE staining and detect Smad2/Smad7 protein with immunohistochemical staining.Results:Compared with normal group, the model group rats alveolitis and pulmonary fibrosis scores were significantly increased;compared with model group,the hormone group,YQYY group,YQYY plus hormone group rats alveolitis and lung fibrosis scores were reduced,and the lung injury of YQYY group reduced obviously.The expression of Smad2 protein of model group in alveolar epithelial cells and the fibroblasts was significantly higher than normal group;compared with model group,the positive expression of Smad2 in hormone group,YQYY group,YQYY plus hormone group were reduced,the Smad2 of YQYY group was the lowest.Compared with normal group,the smad7 protein of model group decreased significantly;compared with model group,Smad7 protein expression in hormone group, YQYY group, YQYY plus hormone group were increased, the Smad7 expression of YQYY group was highest.Conclusion:Yiqiyangyin decoction has a good intervention and therapeutic effect on bleomycin-induced rats pulmonary fibrosis,its mechanism may be related to inhibiting the inflammatory reaction,reduce the formation and deposition of collagen and the intervention of Smad signal pathway.