A 50-year-old woman was reffered to our hospital because of a 7cm mass in the right breast. She had left pectral muscle conserving mastectomy for scirrhous carcinoma nine years earlier. On magnetic resonance imaging, the peripheral zone of the mass was emphasized by using contrast enhancement on Gd-GPTA. Right breast cancer was suspected by an aspiration cytology. She underwent a pectral muscle conserving mastectomy and reconstruction by inserting a tissue expander. The histo-pathological examination showed proliferation of small tumor cells forming trabecular, solid nests with massive necrosis and abundant fibrous stroma. Cellular atypia and nuclear division were also seen and the nuclear grade was rated as 3. Immunohistologically, the tumor cells were positive for Vimentin, S-100 protein and AE1/AE3. From these findings, the tumor was diagnosed as matrix-producing carcinoma.