Excessive oxidative stress is implicated in hepatic fibrogenesis. Extracts of Salvia miltiorrhiza (Sm) have been shown to protect cells against oxidative stress. In this study we investigated the in vitro and in vivo effects of Sm on hepatic fibrosis. A cell line of rat hepatic stellate cells (HSC-T6) was stimulated with transforming growth factor-beta1 (TGF-beta1). The inhibitory effects of Sm (50-400 microg/ml) on TGF-beta1-induced alpha-smooth muscle actin (alpha-SMA) secretion and the mRNA expressions of fibrosis-related genes, including alpha-SMA, connective tissue growth factor (CTGF), and tissue inhibitor of metalloproteinase-1 (TIMP-1), were assessed. Fibrosis was induced by dimethylnitrosamine (DMN) administration in rats. DMN-treated rats were randomly assigned to 1 of 4 groups: saline, Sm (20 mg/kg), Sm (100 mg/kg), or silymarin (100 mg/kg), each given by gavage twice daily for 5 weeks starting from the onset of DMN administration. Sm (200 and 400 microg/ml) significantly inhibited TGF-beta1-stimulated alpha-SMA secretion and the mRNA expressions of alpha-SMA, CTGF, and TIMP-1 in HSC-T6 cells. Fibrosis scores of livers from DMN-treated rats with either a low (1.8 +/- 0.2) or high (1.8 +/- 0.1) dose of Sm, or silymarin (1.4 +/- 0.2) were significantly reduced in comparison with DMN-treated rats receiving saline (3.1 +/- 0.1). Hepatic collagen contents were also significantly reduced by either Sm or silymarin treatment. The mRNA expression levels of alpha-SMA, TGF-beta1, and procollagen I were all attenuated in Sm- and silymarin-treated rats. Moreover, levels of plasma aspartate transaminase activities were reduced by Sm and silymarin treatment. In conclusion, our results show that Sm exerted antifibrotic effects in both HSC-T6 cells and in rats with DMN-induced fibrosis.