In acute pancreatitis, multiple organ failure in the early phase and infectious complications in the late phase are contributors to mortality. To analyze the mechanism of aggravation of acute pancreatitis is to investigate the mechanism of organ dysfunction and infection. As strategy to elucidate the mechanism, various animal experimental models are utilized. Caerulein-induced pancreatitis and bile salt-induced pancreatitis (duct injection model) are frequently employed for mild edematous pancreatitis and severe necrotizing pancreatitis, respectively. It is important to select an appropriate experimental model that corresponds to the purpose of study.