Objective To study the ultrastructure changes in rats with idiopathic pulmonary fibrosis(IPF) induced by bleomycin treated with Fufangbiejia Formula.Methods To divide randomly 180 male SD rats into the sham-operation group(group1),model group(group2),positive control group(group3),groups with high,medium and low dose of Fufangbiejia Formula(group4,5 and 6).On 7~(th),14~(th)and 28~(th) day of the treatment 10 rats every time in every group were randomly selected,anesthelized and sliced up,and the changes of structure and collagen were observed by the light(microscope).The(average) optical density around the bronchi,alveolar nonopaque and compact zones were detected by the(imagine) system.The ultrastructures of the slices were observed by the electron(microscope).Results The result of the light microscope showed that Fufangbiejia Formula relieved the(degree) of pulmonary fibrosis.The imagine analysis showed that there was no significant difference(between) group1 and group2 on 7~(th),14~(th) and 28~(th) day,while there were differences between other groups.The result of the electron(microscope) showed that the content of collagen fibers in group4,5 and 6 were significantly lower than that of group2 and 3 on 7~(th),14~(th) and 28~(th) day.The regional fold,torsion or defection of inophragma,sludging of extracorpuscular base,and the thickening of respiratory tract membrane were less serious in group4,5 and 6 than that in group2 and 3.Conclusion Fufangbiejia Formula can inhibit obviously the accrementition of collagen fibers in rats with idiopathic pulmonary fibrosis.