Objective : Myeongganbo (MGB) composited with Hovenia Semen, Puerariae Radix and Dioscoreae Rhizoma is the prescription for protection of liver function. The purpose of this study was to investigate the effects of MGB extract against acetaminophen (APAP)-induced liver injury in mice. Methods : MGB extract was prepared by extracting with hot distilled water. The extract was freeze-dried following filtration through vacuum distillation system. Mice fasted for overnight were orally administrated with or without MGB extract of different doses (25-200 mg/kg/day). After 30 min, APAP was orally applied with a single dose (400 mg/kg). The levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured in plasmas of mice. Glutathione (GSH), glutathione peroxidase GSH-px), cyclooxygenase-2 (COX-2) activity and tumor necrosis factor-${alpha}$ (TNF-${alpha}$) level were investigated in liver homogenates. Liver sections were stained with haematoxylin & eosin, anti-TNF-${alpha}$ and anti-mouse COX-2 antibodies. Results : APAP treatment remarkably increased AST and ALT activities in plasma but inhibited GSH and GSH-px levels in liver homogenates. Also, liver injury was significantly accelerated by APAP treatment. Furthermore, APAP remarkably elevated COX-2 activity and TNF-${alpha}$ levels in liver homogenates. However, administration of MGB extract was able to counteract these effects. Histological studies provided supportive evidence for biochemical and molecular analysis Conclusions : These results suggest that MGB extract has potent hepatoprotective effect against APAP-induced liver injury, these properties may contribute to liver disease care.