To investigate the underlying mechanism of Shizao Decoction against bleomycin-induced idiopathic pulmonary fibrosis in rats based on the levels of laminin(LN) and platelet-derived growth factor(PDGF).Methods:A total of 96 SPF SD rats were randomized into the blank group，model group，pirfenidone group，and low-dose，medium-dose group，and high-dose Shizao Decoction groups，with 16 in each group.Pulmonary fibrosis was induced in rats by intratracheal injection of bleomycin.From the second day after modeling，rats in the blank group and the model group were given(i.g.) 2 mL normal saline each day and those in the pirfenidone group received(i.g.) 2 mL of pirfenidone solution each day.Moreover，and 2 mL of low-，medium-，and high-concentration of Shizao Decoction was given(i.g.) to the three Shizao Decoction groups，respectively，three times a week，and 2 mL of normal saline was given for the rest of the time.Eight rats(7 in model group and low-dose Shizao Decoction group) were killed in each group on the 14th day and the rest were killed on the 28th day.Lung tissues were collected and the pathological changes were observed based on hematoxylin-eosin(HE) staining.The concentration of LN and PDGF in lung tissues was detected by enzyme-linked immunosorbent assay(ELISA).Results:Compared with the blank group，the model group showed typical pulmonary fibrosis and increase in the concentration of LN and PDGF in lung tissues(P<0.01).Compared with the model group，the administration groups demonstrated significant alleviation of pulmonary fibrosis and obvious reduction in the concentration of LN and PDGF in lung tissues(P<0.01).The concentration of LN and PDGF in lung tissues in high-dose Shizao Decoction group was lower than that in other groups(P<0.01).The levels of LN and PDGF in lung tissues were insignificantly different between the pirphenidone group and the medium-dose Shizao Decoction group(P>0.05).Conclusion:Shizao Decoction relieves the bleomycin-induced pulmonary fibrosis in rats by inhibiting the expression of LN and PDGF in lung tissues.