A 73-year-old woman was referred to our institution due to the presence of narrow and bloody stools. On rectal examination, a rectal mass was observed. Colonoscopy revealed a type 2 tumor in the rectum(RbP)that extended to the dentate line. On biopsy, the tumor was diagnosed as tub1/tub2. No enlarged lymph nodes or metastases were noted on CT. On MRI, the tumor did not invade outside the rectum, and was noted to be proximal to the levator ani muscle. The patient was diagnosed with rectal cancer(cT4a, cN0, cM0, cStage Ⅱb). Preoperative chemoradiotherapy(CRT)was performed to preserve the patient's anus. A total dose of 50.4 Gy of radiation was administered in daily fractions of 1.8 Gy, and chemotherapy was administered with S-1(80 mg/day)orally. Colonoscopy revealed that the tumor significantly reduced in size post-CRT. Further, the boundary between the tumor and levator ani muscle was observed to be more distinct. The patient underwent a laparoscopic intersphincteric resection(D3)+ileostomy. Pathological examination revealed no viable tumor cell in the removed specimen. No tumor recurrence was observed 2 years postoperatively. We report a case in which preoperative CRT for advanced rectal cancer resulted in a pathological complete response.