A 73-year-old woman developed ulcerative colitis with mesalazine intolerance a year ago. She relapsed 10 months later. Although she was in clinical remission with salazosulfapyridine (SASP) and prednisolone administration, she developed agranulocytosis 53 days following SASP administration. She went into septic shock;however, she recovered with antibiotics, granulocyte colony-stimulating factor, and cardiotonic agents. Drug-induced lymphocyte stimulation test was positive for both mesalazine and SASP. Drug selection should be carefully determined in patients with 5-aminosalicylic acid intolerance.