OBJECTIVE: To investigate the potential mechanism by which Shugan Huoxue Huayu Fang (SGHXHYF) ameliorates liver fibrosis. METHODS: Liver fibrosis was induced in rats by intraperitoneal injection of carbon tetrachloride (CCl4) in peanut oil solution (40%, 3 mL/kg body weight) twice a week for 8 weeks. A normal control group received the same volume of peanut oil alone. During weeks 5-8, the CCl4-injected rat groups were administered saline (vehicle control), colchicine (0.1 mg/mL, 1 mg/kg, positive control), or SGHXHYF (0.1 mg/mL; 0.3, 0.6 and 1.2 mg/kg) once daily by oral gavage. Rats were sacrificed 24 h after the last treatment. Blood samples were collected for measurement of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), albumin (ALB), collagen Ⅰ and collagen Ⅲ levels. Liver samples were analyzed by histopathological staining, Masson's staining of extracellular matrix proteins, and immune-ohistochemical staining of αsmooth muscle actin (α-SMA). TGF-ß1/Smad protein and mRNA levels were analyzed by Western blot and quantitative reverse transcription-polymerase chain reaction analysis, respectively. In vitro experiments were also performed using rat hepatic stellate cells (HSCs). RESULTS: Compared with the control animals, CCl4-exposed rats exhibited elevated serum levels of ALT, AST, ALP, collagen I, and collagen III; reduced serum levels of ALB; and increased collagen deposition and αSMA expression in liver sections, reflecting liver fibrosis. CCl4 also increased expression of TGF-ß1 and the activated (phosphorylated) forms of Smad2 and Smad3 but reduced expression of the negative regulator Smad7 in the liver. Notably, concomitant administration of SGHXHYF to CCl4-exposed rats was found to significantly reverse or abolish the pro-fibrotic effects of CCl4 in the liver and reduced serum transferase levels. Analysis of HSCs in vitro confirmed that, mechanistically, SGHXHYF inhibited activation of the TGF-ß1/Smad signaling pathway by downregulating phosphorylated Smad2 and Smad3 and upregulating Smad7 levels. CONCLUSION: SGHXHYF ameliorated CCl4-induced liver fibrosis by inhibiting the TGF-ß1/Smad signaling pathway. These findings suggest that SGHXHYF may have clinical utility for the treatment or prevention of liver fibrosis.