〔Abstract〕 Objective To explore the incidence of major low anterior resection syndrome (LARS) within six months after sphincter-preserving surgery for rectal cancer and to analyze its associated factors. Methods Clinical records, postoperative rehabilitation data and LARS scores were col- lected from 889 patients at 3 months postoperatively and from 844 patients at 6 months postopera- tively. Patients were divided into a major LARS group (3 months postoperatively, n=247; 6 months postoperatively, n=181) and a non-major LARS group (3 months postoperatively, n=642; 6 months postoperatively, n=663). Multivariable logistic regression was used to analyze factors associated with major LARS at 3 and 6 months postoperatively, and the predictive value of the models was assessed using the Hosmer–Lemeshow goodness-of-fit test and the receiver operating characteristic (ROC).Results Among patients undergoing sphincter-preserving surgery for rectal cancer, 247 patients (27.8%) had major LARS at 3 months postoperatively and 181 patients (21.4%) at 6 months postoperatively. Multivariable logistic regression showed that Kegel exercis- es, preoperative radiotherapy, anastomotic leakage, a tumor distance from the anal verge of ≤5 cm, and an anastomotic distance from the anal verge of ≤5 cm were independent factors for major LARS at 3 months postoperatively (P<0.05). At 6 months postoperatively, occasional Kegel exer- cises during 0⁓3 months, Kegel exercises during 4⁓6 months, hydrotherapy during 4⁓6 months, preoperative chemotherapy, a tumor distance from the anal verge of ≤5 cm, and an anastomotic distance from the anal verge of ≤5 cm were independent factors (P<0.05). The models at 3 and 6 months postoperatively showed goodness-of-fit test P values of 0.986 and 0.517 and area under the curve (AUCs) of 0.843 and 0.870, indicating good predictive value. Conclusion The incidence of major LARS within six months after sphincter-preserving surgery for rectal cancer is relatively high, and greater attention should be paid to patients who receive preoperative chemoradiotherapy, develop anastomotic leakage, or have tumor and anastomotic distances from the anal verge of ≤5 cm. Patients should also be advised that early postoperative Kegel exercises and hydrotherapy may reduce the incidence of major LARS.