Objective : Portulaca oleracea (PO) has been used as an important traditional medicine for inflammatory and bacterial diseases in East Asia. However, the protective effects of PO on acute pancreatitis (AP) is not well-known. Therefore, this study was performed to identify the anti-inflammatory and prophylactic effects of PO on cerulein-induced AP. Methods : AP was induced in mice via intraperitoneal injection of supramaximal concentrations of the stable cholecystokinin analogue cerulein ($50{mu}g/kg$) given every hour for 6 times. Water extracts of PO (100, 300, or 500 mg/kg) was administrated intra-peritoneally 1 h prior to the first injection of cerulein. The mice were killed at 6 h after the final cerulein injection. Pancreas and lung were rapidly removed for morphologic and histochemical examination, myeloperoxidase (MPO) assay. Blood samples were taken to determine serum amylase and lipase activities. Results : Administration of PO significantly inhibited pancreatic weight/body weight ratio, pancreas and lung histological injury. And MPO activity which indicates neutrophil infiltration was inhibited by PO extracts on cerulein-induced pancreatitis. In addition, PO administration inhibited digestive enzymes such as serum amylase and lipase activity on cerulein-induced pancreatitis. Conclusion : Our results could suggest that pre-treatment of PO reduces the severity of cerulein-induced AP, thereby, PO could be used as a protective agent against AP. Also, this study could give a clinical basis that PO could be a drug or agent to prevent AP.