A 64-year-old man was admitted to our department with a diagnosis of rectal carcinoma. Preoperative histological diagnosis was highly differentiated adenocarcinoma of Dukes' A classification (Rb', Is', 20-25 mm in diameter, PM'). Preoperative radiation (2.5 Gray/time, total 30 Gray) and chemotherapy (PSK 3g/day x 3 weeks, ACNU 30 mg/m2/week x 3 weeks) were performed on this lesion. After these therapies, form of the tumor changed to IIa', SM', which was recognized by endo-scopic examination with rectal echography. A reduction of the size was 25%. Low anterior resection, curative operation, was performed 2 weeks after the therapy. The resected rectum was examined in detail, resulting in complete disappearance of the carcinoma cell and the tumor was replaced by the inflammatory cells, fibroblasts and granular cells. These findings were compatible with grade IVB of Ohboshi-Simosatos' classification.