We describe here a case of localized polyarteritis nodosa that involved the unilateral breast in a 69-yr-old woman. She presented with a tender breast mass and had suffered for two months. On physical examination, an ill-defined 2 cm sized, firm mass was palpated. Ultrasonographic examination revealed a mass like lesion that contained microcalcifications. The mass was excised because of the suspicion of carcinoma. The histologic findings were vasculitis involving medium and small sized-arteries that showed marked neutrophilic and lymphocytic infiltrations with intimal fibroplasias and fragmentation of the internal elastic lamina. The patient progressed well after surgical excision. The discussion includes the importance of differential diagnosis between localized polyarteritis nodosa and other vasculitis, and review of previously reported cases of vasculitis of the breast. Only 13 cases of polyarteritis nodosa of the breast have been reported and this is the first case of polyarteritis nodosa with mammary duct ectasia.