In low rectal cancer sorgery, the section of rectmn destal to the lower tmnor margin is relaxed and lengthened after fully isolation of the organ. This would facilitate the adoption of anus saving operation. Before and after fully isolation of the recttan in low rectal cancer stwgery, the distance between the lower tmnor margin and the anorectal line was measm-ed by the same rectuscope introduced through the anus. The two results were compared. The average lengthening was less than I cm if the lower tumor marginanorectal line distance was 5 cm. It was 1--2 cm if the lower tmnor margin - anorectal distance was 6 can. I t was more than 2 cm if the distance was 7--9 cm. The loosening and lengthening of the rectal canal was related to the presence of lymphnode metastasis and the skill of the operator. The lengthening was also influenced by the body build of the patient, involvement of the rectal ciraanference and the Dukes stage. Modified Park's operation, trans - resection with anastonmsis of rectmn, and anterior resection on transpubic approach are indicated for those in whom the lower tmnor margin- anorectal line distance was 5 cm. The rectectomy - anastonm6is in the abdominal cavity (Dixon's operation) is indicated for those in whom the lower tmnor margin- anorectal line was 6 cm. If manual anastomosis is difficult, stapling device may be used. The anus saving resection is easy if the distance was 7--9 cm.