Background and AimHepatic cirrhosis is the final stage of liver dysfunction, characterized by diffuse fibrosis, which is the main response to the liver injury. This study is to investigate the effects of ursolic acid (UA) on liver functions and fibrosis in bile duct ligation (BDL) mice and to determine the underlying mechanisms. MethodsCultured hepatocytes were treated with lipopolysaccharide (LPS) in the presence or absence of UA. The reactive oxygen species (ROS) level, protein levels of IB, iNOS and Cox-2, and NF-B activation were detected, respectively. C57/BL6 and AMP-activated protein kinase (AMPK)2(-/-) mice were subjected to BDL for 14 days. UA was administered by gavage. The markers of liver function and oxidative stress, and liver histopathology were analyzed after treatment. ResultsTreatment of hepatocytes with UA dose-dependently activates AMPK, which is abolished by silence of liver kinase B1 (LKB1). LPS significantly increased ROS productions, apoptosis, NF-B activation, and expressions of iNOS and Cox-2 in cultured hepatocytes. All these effects were blocked by co-incubation with UA. Importantly, silence of LKB1, AMPK, or iNOS/Cox-2 by small interference RNA transfection reversed UA-induced effects in cultured cells. In an animal study, 14-day BDL induced liver fibrosis and liver injury, accompanied with increased oxidative stress and protein expressions of iNOS and Cox-2 in liver. Treatment of UA significantly attenuated the BDL-induced detrimental effects in wild-type mice but not in AMPK2(-/-) mice. ConclusionUA via LKB1-AMPK signaling offers protective effects on BDL-induced liver injury in mice, which may be related to inhibition of oxidative stress.