AIM: To investigate the pathway via which 17β-estradiol (β-Est) exerts suppressive effects on rat hepatic fibrosis.METHODS: In vivo study was done in CCl4-induced female hepatofibrotic rats. Fibrosis-suppressive effect of β-Est rat models. Six weeks after the treatment, all the rats were sacrificed and specimens of serum or liver tissue were collected for the studies. Serum liver enzymes,fibrosis markers and estradiol levels were determined by standard enzymatic methods, ELISA and RIA, respectively.Degrees of fibrosis and areas of hepatic stellate cells (HSCs) positive for alpha-smooth muscle actin (α-SMA) in the liver were determined by van Gieson (VG) stain and immunohistochemistry.In vitro studies, HSCs were isolated by a combination of pronase-collagenase perfusion and density gradient centrifugation. First-passage HSCs were randomly divided into 10 groups, and different concentrations of β-Est, 2-hydroxyestradiol (2OHE) or 2-methoxyestradiol (2MeOE) were separately added to the cell groups. After incubation for 72 h, the degree of cell proliferation, collagen production, α-SMA or estrogen receptor (ER) expression was determined by MTT assay, ELISA and immunohistochemistry,respectively.RESULTS: β-Est treatment reduced aspartate aminotransferase (AST), alanine aminotransferase (ALT), hyaluronic acid (HA) and type Ⅳ collagen (C Ⅳ) in sera, suppressed hepatic collagen content, decreased the areas of HSCs positive for α-SMA significantly in both intact and ovariectomized female hepatofibrotic rats. There was a negative correlation between the percentage of fibrotic area of liver tissue and the serum estradiol level; the calculated correlation coefficient was -0.57 (P＜0.01). β-Est and its metabolites concentration-dependently (10-9 mol/L-10-7 mol/L) inhibited HSC proliferation and collagen synthesis. At the concentration of 10-7 mol/L, they could inhibit α-SMA expression. The order of potency was 2MeOE＞2OHE＞β-Est.CONCLUSION: β-Est may suppress hepatic fibrosis probably via its biologically active metabolites.