Acute pancreatitis (AP) severity is determined by associated organ failure (OF). However, enzymatic erosion of peripancreatic vessels can lead to life-threatening hemoperitoneum in clinically non-severe AP without OF. We herein report a case of unexpected hemoperitoneum which developed in a patient with clinically resolving AP without OF. A 36-year-old woman with alcohol use disorder presented with resolving epigastric pain and sustained abdominal distension of 2 weeks’ duration. Ranson’s score on admission was 1 and Computed tomography (CT) revealed non-necrotic AP with peripancreatic fluid collection. She showed sudden hypotension with an abrupt decrease in serum hemoglobin within 24 hours after admission. She was suspected to have an acute hemoperitoneum associated with venous bleeding from AP based on repeated CT. Venous bleeding from the splenic branch was ligated during surgery. The possibility of bleeding at the pancreatic bed should be considered even if the pancreatitis is not severe.