A 29-year-old man with ulcerative colitis presented to the hospital complaining of persistent back pain. Pancreatic enzymes and tumor markers were elevated; imaging showed diffuse narrowing of the main pancreatic duct associated with diffuse pancreatic enlargement. We therefore performed an endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) biopsy of the pancreas using a 19-gauge needle. Histopathology revealed interlobular fibrosis, neutrophil infiltration in the intralobular ducts and acini, and very few immunoglobulin G4-positive cells. The patient was diagnosed with type 2 autoimmune pancreatitis and started on oral steroids; subsequently, we observed an improvement in the pancreatic enlargement and duct narrowing. Histologically proven type 2 autoimmune pancreatitis is rare in Japan.