We reported a case of 30 year-old man who had a mass at left upper abdomen with dull pain. Abdominal ultrasonography, celiac angiography, abdominal computed tomography and laparotomy revealed a pseudocyst, 20×15cm in size, in the spleen. The fibrotic wall of the pseudocyst contained plenty of cholesterol clefts and calcium microscopically. The fluid within it had a high level of amylase activity. Involvement of the spleen by a pancreatic pseudocyst is one of the least common complications of pancreatitis with a total of 21 cases reported in the literature. The consequence may be serious and life-threatening. They include spontaneous splenic rupture, erosion of vessels with sudden hemorrhage and thrombosis of splenic vessels with infarction and frank necrosis. Early diagnosis followed by early surgical intervention with removal of the entire pseudocyst by splenectomy and/or possible distal pancreatectomy is advocated.