Squamous cell carcinoma of the breast is uncommon, but that of the nipple skin is rarer. The effect of chemotherapy in these cases is yet to reach consensus. We report a rare case in which primary squamous cell carcinoma of the nipple skin was successfully treated with S-1 alone. A 64-year-old woman was admitted to our hospital because of a granulomatous tumor mass over the right nipple, which she was aware of for 10 years; the tumor showed a rapid increase in growth before admission. The tumor was approximately 4 cm at the first visit, and was diagnosed as squamous cell carcinoma by incisional biopsy. We administered preoperative systemic chemotherapy owing to the presence of metastasis in an axillary lymph node. After 2 courses of chemotherapy with oralS -1 at 100mg/day for 28 days followed by a 14-day resting period, the primary tumor and metastatic lymph node showed a remarkable reduction in size. The patient subsequently underwent a radical operation and is currently healthy without any recurrence.