A 48 years old man came to our emergency department because of hypotension and syncope after enterocolitis symptom. After admission, anaphylactic symptoms occurred one or two times a day with no allergen. These symptoms disappeared by adrenaline and antihistamines in the short time. He had had small brown exanthemas at his trunk and upper extremities for ten years. Skin biopsy was performed, and he was diagnosed with mastocytosis. Mastocytosis is a disease with a variety of symptoms, and anaphylactic symptoms are one of them. It must be considered for who had idiopathic anaphylactic symptoms with chronic skin lesion.