A 62-year-old woman who visited a neighboring hospital because of a right breast mass was referred to our hospital with a diagnosis of breast cancer with cartilaginous and osseous metaplasia based on a fine needle biopsy. A well-movable tumor 4.5 cm in diameter was palpated in the right AC area. It was revealed as a heterogeneous hypoechoic tumor with a center part with echogenic spots on ultrasonography, and as a high density tumor with coarse calcifications on mammography. Bone scintigraphy showed accumulation of radioactive material at a portion where was identical with the breast tumor. We performed right modified radical mastectomy and sentinel lymph node biopsy. Histopathology disclosed proliferation of spindle-shaped tumor cells and tumor cells showing differentiation toward osteoblast, osteoclast-like giant cells, and chondrocyes ; there were no epithelial components. Accordingly stromal sarcoma with cartilaginous and osseous metaplasia of the breast was diagnosed. The patient experienced lung metastasis and bone metastasis and recurrence one year after the operation. Chemotherapy was unsuccessful and she died one year and eight months after the operation. As this case is of rare stromal sarcoma with prominent cartilaginous and osseous metaplasia, we report this case together with a review of the literature.