Abstract: Objective To evaluate the effect of amygdlin on expression of typeⅠandⅢcollagen in an animal model of pulmonary fibrosis induced by bleomycin. Methods An animal model was established by direct tracheal instillation of bleomycin into rat lungs at tracheostomy.Paraffin-embedded lung sections were stained with H＆E and Sirius red.Histologic changes in the lung were evaluated using light microscopy.Expression of type I andⅢcollagen was detected by polarized light microscopy and quantified by Image-Pro Plus. Results The percentage of typeⅠandⅢcollagen positive area in rat lungs was significantly higher in bleomycin group than in control group after 7,14 and 28 days after establishment of the animal model（P＜0.01）.The percentage of typeⅠ collagen positive area in rat lungs was reduced in amygdlin group 28 days after establishment of the animal model compared with the bleomycin group（P＜0.01）.The percentage of typeⅢcollagen was lower in amygdlin group than in bleomycin at the three time points（P＜0.01）. Conclusion Amygdlin reduce bleomycin-induced increase of typeⅠandⅢcollagen in rat lungs,suggesting that amygdlin can be used in treatment of pulmonary fibrosis in human beings.