Objective To investigate the role of IFN-γ in suppressing bleomycin-induced pulmonary fibrosis in rats.Methods Seventy-five SD rats were randomly divided into five groups (15 rats in each group)，ie.a normal group，a bleomycin-induced pulmonary fibrosis model group，a dexamethasone-treated group，a high-dose IFN-γ-treated group (150 000 U/kg) and a low-dose IFN-γ-treated group (50 000 U/kg).Five rats in each group were randomly killed in 7th day，14th day and 28th day after relative treatment respectively，and lung tissue samples were harvested for histopathology study.HE and Masson staining were used to determine the extent of alveolus inflammation and pulmonary fibrosis respectively.Histoimmunochemical method were adapted to determine protein levels of TGF-β1，CTGF，type Ⅰcollagen and type Ⅲ collagen in pulmonary tissues.Results Histopathological study showed that treatment with either dexamethasone or IFN-γ (both high dose and low dose) remarkably meliorated the extent of alveolus inflammation and suppressed pulmonary fibrosis (compared with model group，all Plt;0.05).Histoimmunochemical study suggested that both dexamethasone and IFN-γ could inhibit the expression of TGF-β1，CTGF，type Ⅰand type Ⅲ collagen (compared with model group，all Plt;0.05)，and the suppression of TGF-β1，type Ⅰand type Ⅲ collagen expression was more obvious in high-dose IFN-γ-treated group than those in low-dose group (Plt;0.05).Conclusions INF-γ possesses apparent anti-fibrosis effect that is similar to dexamethasone but with less side effect.Such effect may resulted from reduced production of type Ⅰand type Ⅲ collagen through expression inhibition of cytokines such as TGF-β1 and CTGF.