Recent reports have demonstrated a negative association between appendectomy and ulcerative colitis. Many retrospective studies have shown that appendectomy appears to be protective against ulcerative colitis. Although the function of appendix is not known, all these studies have suggested that alterations in mucosal immune responses leading to appendicitis or resulting from appendectomy may negatively affect the pathogenic mechanisms of ulcerative colitis. Herein, we report a 45-year-old man who was diagnosed as severe ulcerative colitis 2 years ago. Colonoscopy revealed a feature of pancolitis. He has been treated with several courses of corticosteroids over 2 years. However, dosage of steroid was not tappered down because of the recurrence of symptoms. He was admitted with a diagnosis of acute appendicitis, and underwent appendectomy. Two months after the appendectomy, clinical symptoms and colonoscopic findings improved gradually. Two years after the appendectomy, the patient improved without the recurrences of symptoms, and is stably treated with sulfasalazine alone.