Objective: To investigate the alterations and significances of HMGB1 (high mobility group box-1 protein) and claudin-1 expression in the intestinal mucosal barrier injury caused by severe acute pancreatitis (SAP). Methods: Twenty-four male Wistar rats were equally randomized into sham operation group, SAP model group (model group) and SAP model plus HMGB1 inhibitor ethyl pyruvate (EP) treatment group (EP treatment group). SAP model was induced by retrograde cholangiopancreatic duct injection of 5% sodium taurocholate, and rats in EP treatment group underwent tail veil injection with EP solution 2 h after SAP model establishment. The rats in all groups were sacrificed 24 h after operation, and then the plasma levels of amylase, lipopolysaccharide (LPS) and diamine oxidase (DAO) were determined, the pathological changes of the rat intestinal mucosa were assessed, and claudin-1 protein expression in intestinal mucosa detected by immunohistochemical staining. In addition, the mRNA expressions of HMGB1 and claudin-1 in the bowel tissues were measured by RT-PCR method. Results: Compared with sham operation group, the rats in model group showed significantly increased plasma levels of amylase, LPS and DAO (all P<0.05); intestinal mucosal barrier and intercellular tight junctions of the epithelial cells were damaged; the claudin-1 protein expression in the intestinal mucosa was decreased, and the HMGB1 mRNA expression was increased while claudin-1 mRNA expression was decreased in the intestinal tissues. In EP treatment group, the HMGB1 mRNA expression was increased, and both protein and mRNA expressions of claudin-1 were elevated in the bowel tissues with all the impairment parameters improved versus model group. Conclusion: The increased HMGB1 expression in the intestinal tissue which results in the down-regulation of tight junction protein claudin-1 is probably responsible for SAP induced intestinal mucosal barrier injury. HMGB 1inhibitor EP has protective effect against SAP induced intestinal mucosal barrier injury.