Objective:To investigate the application value of three-dimensional (3D) laparoscope in the transanal total mesorectal excision (TaTME).Methods:The retrospective cohort study was conducted. The clinicopathological data of 20 patients with middle and low rectal cancer who underwent TaTME in the Ruijin Hospital Affiliated to Shanghai Jiaotong University School of Medicine from June 2018 to October 2019 were collected. There were 15 males and 5 females, aged from 28 to 81 years, with a median age of 64 years. Of the 20 patients, 10 patients using 3D laparoscopic system for transanal approach of TaTME were divided into 3D group, and 10 patients using two-dimensional (2D) laparoscopic system for transanal approach of TaTME were divided into 2D group. Observation indicators: (1) intraoperative situations and postoperative recovery; (2) postoperative pathological examination; (3) follow-up. Follow-up was conducted by outpatient examination and telephone interview to detect survival of patients and recurrence and metastasis of tumors in patients up to April 2020. Measurement data with skewed distribution were represented as M (range), and comparison between groups was analyzed using the Mann-Whitney U test. Count data were described as absolute numbers, and comparison between groups was analyzed using the Fisher exact propability. Comparison of ordinal data was analyzed using the Mann-Whitney U test. Results:(1) Intraoperative situations and postoperative recovery: patients in the two groups completed surgeries successfully, without tranversion to laparostomy from laparoscopic surgery, transversion to transabdominal surgery from transanal surgery, or intraoperative death. The cases with terminal ileostomy, cases with manual anstomosis or mechanical anastomosis (anastomotic methods), operation time, volume of intra-operative blood loss, duration of postoperative hospital stay, cases with anastomotic leakage or anastomotic hemorrahge (postoperative short-term complications), cases with anastomotic stenosis of the 3D group were 7, 4, 6, 150 minutes (range, 100-220 minutes), 50 mL (range, 30-100 mL), 8.5 days (range, 7.0-16.0 days), 2, 0, 1, respectively, versus 8, 5, 5, 180 minutes (range, 120-250 minutes), 100 mL (range, 30-200 mL), 9.5 days (range, 6.0-17.0 days), 1, 1, 1 of the 2D group. There was no significant difference in the terminal ileostomy, anastomotic methods, postoperative short-term complications, or anastomotic stenosis between the two groups ( P>0.05). There was no significant difference in the operation time, volume of intraoperative blood loss, or duration of postoperative hospital stay between the two groups ( Z=1.909, 1.827, 0.687, P>0.05). Patients with short-term complications in the two groups were improved after conservative treatments. There was 1 patient with anastomotic stenosis in either group, and they were improved after endoscopic balloon dilatation. (2) Postoperative pathological examination: the maximum tumor diameter, distal margin of the tumor, the number of lymph nodes harvested, cases with cancer nodes in the mesentery, cases with complete mesentery or median complete mesentery (the integrity of mesentery), cases in stage Ⅰ, Ⅱ, Ⅲ (postoperative pathological stage) of the 3D group were 3.8 cm (range, 1.8-5.0 cm), 1.0 cm (range, 0.5-2.5 cm), 14.5 (range, 6.0-19.0), 1, 9, 1, 4, 2, 4, respectively, versus 4.8 cm (range, 1.0-8.5 cm), 0.8 cm (range, 0.3-1.5 cm), 15.5 (range, 8.0-18.0), 1, 8, 2, 2, 4, 4 of the 2D group. There was no significant difference in the maximum tumor diameter, distal margin of the tumor, the number of lymph nodes harvested, the integrity of mesentery, or postoperative pathological stage between the two groups ( Z=1.673, 1.772, 0.038, 0.610, 0.482, P>0.05). There was no significant difference in the cases with cancer nodes in the mesentery between the two groups ( P>0.05). Patients in the two groups had negative distal margin and circumferential margin. (3) Follow-up: patients in the 3D group and 2D group were followed up for 11 months (range, 6-16 months) and 13 months (range, 6-21 months), respectively. During the follow-up, there was no local recurrence, distal metastasis, or tumor-related death. Conclusions:3D laparoscope applied in the TaTME can achieve similar clinical efficacy with 2D laparoscope, which may have a positive impact on the operation time and volume of intraoperative blood loss.