A case of endocrine ductal carcinoma of the breast is presented. A 65-year-old woman was admitted with complaints of left breast mass and pain. Physical examination, mammography, ultrasonography, and computed tomography showed a mass 5 cm in diameter in the left breast suggestive of breast cancer, and incisional biopsy confirmed ductal carcinoma. Auchincloss's mastectomy was performed. The tumor, 4.0 x 3.8 cm in size, consisted of a relatively uniform proliferation of tumor cells with round nuclei and abundant eosinophilic cytoplasm. Immunohistochemically, tumors cells were positive for chromogranin A, synaptophysin, and neuron-specific enolase. Endocrine ductal carcinoma with invasion was diagnosed. No lymph node metastasis was observed, and estrogen and progesterone receptors were positive.