Therapy with oral 5-aminosalicylic acid (5-ASA) for uicerative colitis has been reported to be effective and safe. We describe a case of biochemically proven mild acute pancreatitis occurring after 9 d of oral 5-ASA therapy for uicerative colitis. A hypersensitivity mechanism seemed to be involved in the development of pancreatitis probably owing to erratic systemic absorption of the drug. We suggest clinical and biochemical monitoring for early diagnosis of pancreatitis in patients with uicerative colitis receiving 5-ASA administration. This is the first report of acute pancreatitis developed by oral 5-ASA therapy for the treatment of uicerative colitis in the literature of Japan.