A 54-year-old man presented with an enlarged left (lt) lateral lymph node (LLN), which was detected by magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET-CT). Endoscopic examination of the colon revealed the presence of a type 1 tumor, 20mm in diameter, in the lower rectum; the tumor was diagnosed as a well-differentiated adenocarcinoma (tub1). The patient received combined neoadjuvant chemoradiotherapy (nCRT)with S- 1 for treatment of the rectal cancer and LLN metastasis (MP, T2N3M0, Stage IIIb). S-1 was administered orally at a dose of 120 mg/day on days 1-14, and 22-35; a total dose of 45 Gy was delivered (1.8 Gy/day, for 25 days). Upon nCRT, there was a remarkable reduction in the tumor size, the primary tumor receded, and the LLN decreased from 16 mm to 8 mm in diameter. The maximum standardized uptake value (SUVmax) also decreased from 3.8 to 1.9 on PET-CT. Six weeks after nCRT, ultralow anterior resection and bilateral lymph node dissections were performed. Histopathological examination showed a partial presence of cancer cells in the scarred primary tumor; however, no viable cancer cells were observed in the lt. LLN.