Abstract: OBJECTIVE To investigate the protective effect of anti-pulmonary fibrosis active extract from Periplaneta Americana(ML-HB) on bleomycin-induced pulmonary fibrosis in rats. METHODS Male SD rats were randomly divided into normal group, model group, positive group(dexamethasone, 3 mg·kg^-1, qd) and ML-HB high, middle and low dosages groups (120, 60, 30 mg·kg^-1, qd). The pulmonary fibrosis model was established through tracheotomy with bleomycin(5 mg·kg^-1). The rats were intervened by treating with intraperitoneal administration after modeling 24 h. The rats were sacrificed on the 30th day after administration, lung index was determined, tumor necrosis factor-α(TNF-α) and transforming growth factor-β1(TGF-β1) in lung homogenate were detected by ELISA, hydroxyproline(HYP) was detected by UV, the inflammatory lesions of lung tissue was observed by HE staining, the degree of pulmonary fibrosis was determined by Masson staining, and α-smooth muscle actin(α-SMA) and type I collagen(COL-I) were observed by immunohistochemical staining. RESULTS Compared with the normal group, the model group showed higher lung index, and higher expression of TNF-α, TGF-β1 and HYP(P<0.05 or P<0.01), lung tissue inflammation and pulmonary fibrosis were serious, α-SMA and COL-I expression were elevated. Compared with the model group, the ML-HB middle dosage group showed lower lung index, and lower expression of TNF-α, TGF-β1, and HYP(P<0.05 or P<0.01), lung tissue inflammation and pulmonary fibrosis were alleviated, α-SMA and COL-I expression were decreased. CONCLUSION ML-HB can reduce the expression of TNF-α, TGF-β1, HYP, α-SMA and COL-I, and delay lung tissue lesions, interfere with the further development of fibrosis.