Objective To investigate the expression of cyclooxygenase-2 (COX-2) in liver tissue of severe acute pancreatitis (SAP) rats. Methods A rat model of SAP was induced by retrograde infusion of 3.5% sodium taurocholate into the biliary-pancreatic duct. Eighty rats were randomly divided into SAP group and control group. The levels of serum amylase (AMY), alanine aminotransferase (ALT), aspartate aminotransferase (AST), tumor necrosis factor (TNF) -α and ascites AMY were detected dynamically at 4 h, 8 h, 16 h and 24 h after operation. The pancreatic and liver injuries were observed by light microscope. The expression of COX-2 in liver tissue was measured by immunohistochemistry. Results Compared with the control group, the levels of serum AMY, ALT, AST, TNF-α and ascites AMY increased significantly at the time point of 4 h, 8 h, 16 h and 24 h (Plt;0.05). These changes were paralleled with the histopathological changes of pancreatic and liver tissue. The expression positive rates of COX-2 at the different time in the SAP group were higer than those of the control group (Plt;0.05). There was a significantly positive correlation between the expression of COX-2 and ALT (rs=0.949, P=0.039), AST (rs=0.972, P=0.016) and serum AMY (rs=0.944, P=0.041), respectively. Conclusion Overexpression of COX-2 may play an important role in liver injury during SAP.