Salvia miltiorrhiza （Sm） is a traditional herbal medicine with multiple effects on various diseases. Its water-soluble parts have been used to produce injectional powder. In this study, liver fibrosis rats were induced by intraperitoneal injection of dimethylnitrosarnine for 3 consecutive days per week for 4 weeks. After 2 weeks, rats in the positive drug group were subcutaneously injected with 8×10^5 IU/kg IFNα2b, while the Sm treatment groups were intraperitoneally injected with 50, 100 and 200 mg/kg solution of Sm injectional powder, respectively, for 6 days per week for 4 weeks. The results showed that either IFNα2b or the Sm injectional powder significantly increased the body weight and liver to spleen ratio, and three doses of the powder brought down the spleen index. Serum analysis showed that both IFNα2b and the Sm powder reduced levels of alanine transaminase and total bilirubin, while only 100 and 200 mg/kg of the Sm powder ameliorated aspartate transaminase and albumin levels. In the collagen examination, reduced hyaluronic acid and procollagen type III levels, less fibrous hyperplasia and collagen deposits, and improved hepatocyte states were clearly observed in rats treated with either IFNα2b or Sm injectional powder. In addition, the mechanism of action of the Sm powder was also studied. Immunohistochemical staining showed that IFNα2b and Sm injectional powder significantly down-regulated the expression of transforming growth factor-β1 （TGF-β1） and platelet derived growth factor （PDGF）. In conclusion, Sm injectional powder has protective effects on dimethylnitrosamine-initiated liver fibrosis in rats, and the mechanism may include the down-regulation of TGF-β1 and PDGF.
