A 46-year-old man was admitted to our hospital for further evaluation of a hypoechogenic mass in the pancreatic body. He had no history of hypertension, pancreatitis, abdominal trauma, or portal hypertension. He had no abdominal symptoms. A contrast-enhanced CT scan demonstrated a hypodense, round shaped mass. EUS and MRI also showed it to be a pancreatic mass. Because of the tumor size of more than 30mm and the possibility of malignancy, distal pancreatectomy was performed. Microscopic findings showed the mass was the dissection of the proximal splenic artery. The true lumen of the dissecting aneurysm was occluded and the false lumen developed fusiform dilatation. Moreover, microscopic findings revealed the rupture of the false lumen complicated by pseudoaneurysm. We finally diagnosed the lesion simulating a pancreatic tumor as the pseudoaneurysm of the splenic artery.