A 64-year-old woman presented with abdominal pain, upper gastrointestinal bleeding, and purpura on her face and extremities. She had previously been treated with mesalazine for ulcerative colitis. Tests revealed anaemia, elevated inflammatory markers (erythrocyte sedimentation rate, 82 mm/h; C-reactive protein concentration, 13.05 mg/dL), and a high proteinase 3-specific antineutrophil cytoplasmic antibody level (94.8 U/mL). Computed tomography showed oedematous thickening of the intestinal wall from the ascending colon to the sigmoid colon. Colonoscopy revealed inflammation of the leukocytoclastic vasculitis, consistent with granulomatosis with polyangiitis mucosa, and the sigmoid colon had various ulcers with mucosal inflammation. Skin biopsy revealed leukocytoclastic vasculitis, indicative of granulomatosis with polyangiitis. Prednisolone (40 mg/day) and tacrolimus (4 mg) resolved the symptoms. To our knowledge, this is the first report of successful tacrolimus therapy for ulcerative colitis complicated by granulomatosis with polyangiitis.