A 68-year-old patient with advanced oral squamous cell carcinoma (T3N2bM0, Stage IVA) was treated by concurrent radiotherapy with S-1.S-1 (120 mg/body/day) was orally administered for 4 weeks followed by a 2-week rest period as one course, and radiation was given (1.8 Gy/day; 5 days/week) for a total of 61.2 Gy. After 61.2 Gy radiation and two courses of S-1, the primary region showed a complete response (CR), and that the tumor cell was not identified as a result of biopsy. In addition, the metastatic lymph nodes in the neck were no longer seen on head and neck computed tomography (CT). Although the patient is still taking UFT, he is well with no signs of recurrence 27 months from the initial treatment.