Neoadjuvant chemoradiotherapy has been recommended as the standard preoperative treatment for locally advanced rectal cancer. However, preoperative radiotherapy increases the risk of bowel dysfunction after sphincter-preserving surgery, for which patients suffer from incontinence, urgency, and unpredictability defecation problems. Furthermore, preoperative chemoradiotherapy is a potential risk factor of anastomotic leakage and stenosis after rectal cancer surgery. Unhealthy anastomosis, with both ends of injured bowel segments after pelvic radiation, is a major concern. When conventional surgical procedures would retain part of sigmoid colon that has been included in the radiation target, sphincter-preserving surgery with proximally extended resection margin could provide an intact proximal colon limb for the anastomosis. It is not known yet whether proximally extended resection improves postoperative bowel function or anastomotic integrity for patients with rectal cancer after neoadjuvant chemoradiotherapy. The proposed study will compare sphincter-preserving surgery with and without proximally extended resection margin, to observe the postoperative bowel function, as well as the incidence of anastomotic complication. This study will examine a new surgical strategy, which potentially benefits the patients undergoing neoadjuvant chemoradiotherapy.