Ulcerative colitis (UC) has been known as inflammatory bowel disease. Progress in UC management strategies has led to optimized approaches for achieving the two primary clinical goals of therapy: induction and maintenance of remission. We here review about immunosuppressants in management of UC; Cyclosporine A (CsA) has been used for the induction therapy in steroid resistant refractory UC. Although it has been reported that CsA has high response rate in severe UC, long-term efficacy (maintenance of remission) has not been proven. To improve maintenance therapy, immunosuppressant has been re-considered in management of UC. In recent years, it has been reported that efficacy of 6-mercaptopurine/azathioprine in maintenance of remission of UC is superior to 5-aminosalicylate (5-ASA). Pharmacological studies have indicated thiopurine methyltransferase (TPMT) activity is essential for maintenance of blood concentration of 6-thioguanine nucleotide (6-TG).