A case of angiosarcoma of the breast which is rare and carries the worst prognosis of any breast malig-nancies is presented. A 42-year-old housekeeper was admitted to the hospital because of a painful and elastic hard tumor with ill-defined margin and 5×5cm in diameter in her left breast. Incisional biopsy was per-formed and the tumor was diagnosed as a lymphangioma, so she was discharged. Two years later, she was admitted again with the same symptom as those in two years ago. The tumor size increased to 6×6cm in diameter and a color of the skin over the tumor is changed to dark purple tone. Aspiration biopsy from the tumor revealed class IV. Consequently a modified radical mastectomy and axillary dissection were performed with a suspicion of malignant breast tumor. Pathological findings revealed that the tumor was angiosarcoma of the breast. After the operation multi-disciplinary treatment including systemic administration of interleukin 2 was carried out, but in vain. She experienced metastasis 13 months after the operation and died from tumor metastasis. An autopsy disclosed metastasis to the liver, adrenal gland and bone.