AIM: To investigate effects of pioglitazone on rat hepatic fibrosis and to explore its mechanism.METHODS: Rat hepatic fibrosis was induced by carbon tet:achloride (CCl4). Forty Sprague-Dawley rats were divided randomly into 4 groups: control, model, and two treatment (PⅠ, PⅡ) groups. Except for rats in control group, all rats were given subcutaneous injection of 400 mL/L CCl4, twice a wk for 8 wk. Rats in PⅠ and PⅡ groups were also treated with pioglitazone of 3 mg/kg, daily via gastrogavage beginning on the 1st day and at the end of the 2nd week,administration of CCl4 respectively. Liver functions (ALT,AST), serum fibrotic markers (HA, LN, PCⅢ) and hepatic hydroxyproline (HP) concentration were determined respectively. Histochemical staining of formalin-fixed liver sections with HE, Masson-Trichrome, and immunohistochemical staining for α-smooth muscle actin (α-SMA) were performed.Modified Knodell and Chevallier semi-quantitative scoring system (SSS) was used to evaluate necroinflammatory activity and fibrosis degree.RESULTS: Compared with model group, pioglitazone significantly reduced the serum levels of ALT, AST, HA, LN and PCⅢ (P＜0.05 or ＜0.01). The HP concentrations in PⅠ (210.90±24.07 μg/g), and PⅡ (257.36±30.55 μg/g) groups were also lower than those in model group (317.80±36.44 μg/g) (P＜0.01). Histologic examination showed that PⅠ and PⅡ groups had milder hepatocellular degeneration, necrosis and infiltration of inflammatory cells, and thinner or less fibrotic septa than did model group. The scores for necroinflammation in PⅠ (2.80±1.03), and PⅡ (3.00±1.05) groups were significantly reduced as compared with model group (4.88±2.30) (P＜0.05 or ＜0.01); the fibrosis scores in PⅠ (3.40±1.65), and PⅡ (4.60±1.35) groups were also markedly lower than those in model group (7.00±3.21)(P＜0.05 or ＜0.01). Immunohistochemical staining showed that expression of α-SMA in PⅠ and PⅡ groups was ameliorated dramatically compared with model group.CONCLUSION: PPARγ agonist pioglitazone greatly retards the progression of rat hepatic fibrosis induced by CCl4through inhibition of HSC activation and amelioration of hepatocyte necroinflammation in rats.