Primary leiomyosarcoma of the breast is an extremely rare tumor, accounting for less than 1% of all breast tumors and only 24 cases have been reported in the English medical journals. It is quite difficult to diagnose leiomyosarcoma preoperatively. Establishing an accurate diagnosis is very important in planning treatment. When preoperative diagnosis can be achieved before or during the operation, wide resection should be performed. There is no need for axillary lymph node dissection. In this case report, we present a case involving primary leiomysarcoma of the breast in a 48-year-old woman and we discuss optimal treatment options.