Objective: To investigate the protective effect of sinomenine against liver injury caused by obstructive jaundice in rats. Methods: Thirty-two rats were equally randomized into sham operation group, model group, and low- and high-dose sinomenine treatment group. Except for the sham operation group, rats in all other groups underwent 1igation of the common bile duct. From the first day after surgery, rats of the two sinomenine treatment groups were given sinomenine (40 or 80 mg/kg) daily by gavage administration, and rats of the sham operation group and model group were given normal saline of the same volume instead. All rats were sacrificed on the postoperative day 8, the serum levels of total bilirubin (TBIL), direct bilirubin (DBIL), alanine aminotransferase (AST) and aspartate aminotransferase (ALT) were measured in blood samples drawn from their abdominal aortas, their right hemi-livers were used for determination of the contents of malondialdehyde (MDA) and myeloperoxidase (MPO), and total antioxidant capacity (T-AOC) by using commercial kits, as well as the gene expression of transforming growth factor β1 (TGF-β1) by real-time PCR technique; left hemi-livers were used for histopatological examination and detection of TGF-β1 protein expression through H&E and histoimmunochemical staining, respectively. Results: Except for the sham operation group, the rats’ liver tissues of all other groups presented varying degrees of pathological changes, and among them, the pathological changes of both sinomenine treatment groups were milder than those of the model group. Compared with the sham operation group, in all other groups, the serum levels of TBIL, DBIL, ALT and AST increased significantly, the liver tissue contents of MDA and MPO increased but T-AOC decreased significantly, and both gene and protein expression of TGF-β1 in liver tissues increased significantly (all P<0.05). The changes of above listed parameters were all more evident in model group than those in the two sinomenine treatment groups (all P<0.05), but all had no significant differences between the two sinomenine treatment groups (all P>0.05). Conclusion: Sinomenine has protective effect against liver damage caused by obstructive jaundice, and the mechanism may be probably related to its reducing the expression of TGF-β1.