We describe a case of locally recurrent rectal cancer that was successfully treated with radiation and chemotherapy with S-1; this treatment resulted in long-term survival of the patient with a good performance status. A 51-year-old man underwent Hartmann's operation for advanced rectal cancer. At 6 months after the surgery, a pelvic computed tomography (CT) scan showed a local recurrence of the rectal cancer. The patient's serum CA19-9 level had increased to 3,200 U/mL. The tumor was unresectable, so that radiation therapy was administered to the pelvic region at a total dose of 56 Gy, followed by oral chemotherapy with S-1 for 2 years. After these treatments, the serum CA19-9 level returned to normal. No signs of tumor recurrence were observed as of 3 years and 5 months after the confirmation of local recurrence. A combination of radiation therapy and oral administration of S-1 could be a useful treatment for unresectable locally recurrent rectal cancer.