A resected case of complete response after treatment with S-1 for recurrent squamous cell carcinoma component of the breast is presented.A 65-year-old woman was admitted to another hospital because of a left breast tumor. A tumor approximately 6 cm in diameter was palpable in the subareolar-lower (DBE) region of the left breast; the diagnosis was breast cancer. We performed mastectomy and axillary lymph node dissection. The pathological diagnosis revealed squamous cell carcinoma of the left breast(pT3N1M0, Stage III A). FEC chemotherapy, a standard chemotherapy regimen for general breast cancer, was performed as first-line adjuvant therapy, but was withdrawn after 1 course due to sepsis shock. Weekly PTX chemotherapy as second-line treatment was also withdrawn after six courses due to interstitial pneumonia. Few skin rashes were observed along the incision scar of the left breast, but biopsy revealed skin invasion by local recurrence of squamous cell carcinoma of the breast. Treatment with S-1 was performed for 8 months, and she underwent resection of left skin, fat tissue, and underlying muscle, including the recurrent region. No residual primary carcinoma foci was found in the resected specimen; therefore, the pathological diagnosis revealed complete response for the squamous cell carcinoma component.