Carcinoma ex pleomorphic adenoma (CEPA) is a carcinoma that shows histologic evidence of arising in or from a benign pleomorphic adenoma. Carcinoma ex pleomorphic adenoma often occurs in parotid glands, but is extremely rarely in the tongue. A 53-year-old Japanese woman was referred to the Department of Oral and Maxillofacial Surgery, Nagasaki University Hospital, because of tumor of the right dorsum tongue. She had a history of surgery of breast cancer (invasive ductal carcinoma) and it was disseminated to the lung and bone. Macroscopic examination revealed an oval tumor with a smooth mucosal surface of 10 mm in diameter in the right dorsum tongue. A clinical diagnosis was metastasis from breast cancer or primary salivary gland tumor. Histologic diagnosis of the biopsy specimen was CEPA. She underwent partial glossectomy under general anesthesia. The final diagnosis of surgical materials was CEPA based on the differential diagnosis from breast carcinoma. She is alive bearing disseminated breast carcinoma without recurrence of CEPA at 6 months after glossectomy.