To investigate mechanism of action of Biejia Pill on rats with Bleomycin- induced pulmonary fibrosis.Methods:Fifty SD rats were randomized to 5 groups: model group, saline group, Prednisone Acetate group, medium dose Biejia Pill group, and high dose Biejia Pill group. The rat model of pulmonary fibrosis was established using Bleomycin. On Day28, TGF-β₁, smad₃ and smad₇ in lung tissues were assessed using SABC methods.Results:In medium dose and high dose Biejia Pill groups, TGF-β₁ expression decreased, smad₇ expression increased. In high dose Biejia Pill group, smad₃ expression decreased.Conclusion:Biejia Pill can reduce Bleomycin induced pulmonary fibrosis in rats, the mechanism of which is related to regulation of TGF-β₁, smad_3/7 expression.