Abstract: Objective To explore the effects of endoscopic submucosal dissection (ESD) and endoscopic mucosal resection (EMR) on the surgical results and complications of patients with early colorectal cancer (CRC) and precancerous lesions. 
Methods Retrospective analysis was performed on 120 patients with early CRC and precancerous lesions treated in our hospital, who were divided into a control group (n=55) and an observation group (n=65) according to surgical methods. Patients in the control group underwent EMR, and patients in the observation group underwent ESD. The surgical indicators of the two groups were compared, the oxidative stress level of the two groups before surgery and at 7 d after surgery was observed. The patients were followed up for 6 months after surgery, and the quality of life before and after surgery was compared. The occurrence of perforation, infection and bleeding after surgery and presence of recurrence of patients within 6 months after surgery were recorded. 
Results Compared with the control group, the duration of operation and intraoperative bleeding was longer or more, and the thickness of the resected specimen and the wound diameter were greater than those in the control group, suggesting significant difference (P＜0.05). The total resection rate and curative resection rate (58.46%) were higher than those in the control group (60.00%, 46.63%), but the difference was not statistically significant (P＞0.05). After treatment, the malondialdehyde (MDA), glutathione disulfide (GSSG), cortisol (Cor) levels all increased, which were statistically different (P＜0.05), but the difference between two groups was not statistically significant (P>0.05). The differences in the evaluation results of various dimensions of quality of life between two groups before surgery were not statistically significant (P＞0.05). After treatment, the quality of life of the patients at 3 months after surgery was evaluated again; the quality of life score was improved, and the increase in the observation group was higher than that in the control group (P＜0.05). The incidence of perforation, intraoperative bleeding and infection in the observation group was 12.31%, which was lower than that in the control group (34.55%). Within 6 months after surgery, 1 case (1.54%) in the observation group had recurrence, which was significantly different from that (8, 14.55%) in the control group (P＜0.05). 
Conclusion Compared with EMR, it is more difficult to perform ESD for patients with early CRC and precancerous lesions, with longer duration of operation. However, the level of oxidative stress of patients after surgery changes fairly, which can effectively reduce the recurrence rate of patients after surgery, reduce the occurrence of postoperative complications, and improve the quality of life of patients. 

Key words: olorectal neoplasms, precancerous conditions, endoscopic mucosal resection