A 54-year-old Japanese man noticed painful swelling and redness of his left leg. He was admitted for treatment of cellulitis, which was accompanied with increased anti-streptolysin O and anti-streptokinase titers in his clinical course. After Piperacillin/Tazobactam administration, the skin lesion resolved. However, the patient then developed arthritis, palpable purpura, and intermittent abdominal pain, later found to be secondary to a severe duodenal ulcer. He was diagnosed with cellulitis-associated anaphylactoid purpura and was given prednisolone, which dramatically improved his symptoms. The anaphylactoid purpura was likely caused by Streptococcus-induced cellulitis, which was successfully treated with prednisolone. Association between these diseases is rare.