We report a case of primary giant cell malignant fibrous histiocytoma (GCMFH) of the breast. A 56-year-old Japanese woman presented with a firm mass in the right breast. Mammography and ultrasonography revealed a well-circumscribed and lobulated mass in the upper outer quadrant of the right breast, indicative of a benign breast tumor or mucinous carcinoma. Magnetic resonance imaging revealed a restricted breast tumor without intraductal spread. Computed tomography and bone scintigraphy found no sites of distant metastases. Fine needle aspiration biopsy showed several clusters of atypical cells associated with numerous multinucleated giant cells. Breast-conserving surgery with axillary lymph nodes dissection was performed. Histological examination showed primary GCMFH of the breast. No metastases were identified in any of the 15 left axillary lymph nodes resected and surgical margins were free from tumor cells. The tumor was negative for both estrogen and progesterone receptor. Neither adjuvant chemoendocrine therapy nor postoperative radiotherapy was given, and the patient has remained disease free for 30 months postoperatively. To our knowledge, only 30 cases of primary MFH of the breast have been reported in the literature.