We report a case of giant breast angiosarcoma. A 20-year-old woman noticed enlargement of her rightbreastandconsultedherfamilydoctor.Thesymptomhadbeenstablefor4months.Granulomatous mastitiswassuspected.However,shecomplainedthattheenlargementhadbecomerapid,andshewas referredtoourhospital.Herrightbreastwasfoundtohaveswollento20cmindiameterandhadsubcutaneous hemorrhages. Breast ultrasound revealed a tumor in the entire right breast, with a heterogeneousechoiclesionandinternalbloodflowsignals.ContrastCTandMRIimagesdemonstratedatumor shadowwithpartialcontrasteffectoccupyingtheentirerightmammarygland.Therewasnodistantorganmetastasis.Basedoncarefulcoreneedlebiopsy,thetumorwasdiagnosedasanangiosarcoma.She underwenttotalmastectomywithexcisionoftheoverlyingskinandthepectoralismajormuscle,anddissectionoftheaxillarylymphnodes.Theskindefectwasreconstructedwithalatissimusdorsimyocutaneous flap. Post-mastectomy radiation therapy was performed on the chest wall, and no other adjuvant therapywasscheduled.Approximately2yearsaftertreatment,shewasfreeofrecurrence.Herein,we reportacaseofbreastangiosarcoma,discussit,andreviewtheliterature.