The patient was an 80-year-old woman who was diagnosed with locally advanced low rectal cancer. It was unresectable and we performed chemoradiotherapy combined with S-1 (S-1 80 mg/m2, RT 1.8 Gy × 25, total 45 Gy). An effective reduction of primary region resulted in curative resection (super low anterior resection, D3 lymph node dissection, covering ileostomy) with preserving the anal sphincter. Histopathologically, therapeutic efficacy was Grade 2. Preoperative chemoradiation has been a standard therapy in Western countries and would control local recurrence. This case indicated that CRT could improve a rate of curative resection in patients with locally advanced rectal carcinomas.