A 77-year-old man suffered from acute pancreatitis during the treatment of relapsed acute promyelocytic leukemia with As2O3. He presented with epigastralgia on day 25 during the treatment with As2O3. Pancreatic enzyme levels were elevated and the computed tomography scan of the abdomen showed swelling of the pancreas. As acute pancreatitis due to As2O3 was suspected, As2O3 was discontinued. Intravenous gabexate mesilate was administered, and the pancreatitis improved. Acute pancreatitis should be considered as a possible complication during treatment with As2O3.