Melatonin has been reported to inhibit hepatic fibrosis and the mechanism may be correlated to its anti-oxidant effect.Nevertheless,the mechanism is not completely identified.This study was conducted to investigate the effects of melatonin on TGF-β1/Smad signaling pathway in liver fibrosis in rats.The liver fibrosis model was made by the subcutaneous injection of CCl4.The liver pathology changes were detected using hematoxylin and eosin (H&E) staining and Van Gieson (VG) staining.Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities were measured with an autoanalyzer.Glutathione peroxidase (GPx) activities and levels of malondialdehyde (MDA) and hydroxyproline (Hyp) in liver were evaluated by spectrophotometry.Expression levels of TGF-β1,Smad2/3,phosphorylated Smad2/3 (p-Smad2/3) and Smad7 in liver were detected by immunohistochemistry and West blot analysis.Results showed that melatonin suppressed CC14-induced liver fibrosis,along with an improvement in histological changes,significant decreases in pathologic grading sores and obvious decreases in Hyp levels in liver.Melatonin improved liver function indicated by decreased serum ALT and AST activities.In addition,melatonin exerted its anti-oxidant effects,as supported by decreased MDA levels and increased GPx activities in liver.Furthermore,melatonin inhibited TGF-β1/Smad pathway,as evidenced by decreased TGF-β1,Smad2/3 and p-Smad2/3 expression and increased Smad7 expression in liver.In conclusion,melatonin may suppress CCl4-induced hepatic fibrosis in rats via inhibiting TGF-β1/Smad pathway.It is possible for melatonin to be a potential reagent to treat and cure liver fibrosis.