Autoimmune pancreatitis (AIP) is frequently associated with inflammatory bowel disease in Western countries, but such cases are rare in Japan. Here, we report a Japanese case of AIP with ulcerative colitis. A 34‐year‐old Japanese man was admitted to the Hospital of Shiga University of Medical Science with severe back pain. He received total colectomy due to a severe attack of ulcerative colitis 16 months before. Laboratory studies on admission indicated elevation of serum amylase and lipase levels. Serum immunoglobulin (Ig)G and IgG4 levels were within normal range, and antinuclear antibody and rheumatoid factor were negative. Ultrasonography and contrast‐enhanced computed tomography (CT) showed a diffuse swelling of the pancreas with main pancreatic duct dilatation. Endoscopic retrograde cholangiopancreatography demonstrated segmental narrowing of the main pancreatic duct in the pancreatic head with distal dilatation. Aspiration and brushing cytology revealed no malignancy. No abnormal finding was observed in the common bile duct. He was diagnosed with AIP and treated with 30 mg predonisolone daily. After predonisolone therapy, back pain rapidly disappeared, and serum elevation of pancreatic enzymes returned to normal range. This case is an unusual type of AIP in Japan.