Objective To investigate the characteristics of learning curve of intraoperative nerve monitoring in endoscopic thyroidectomy via sternomastoid pathway. Methods The data of 42 patients who underwent endoscopic thyroidectomy via sternomastoid pathway were retrospectively analyzed. All the operations were performed by the same group of operators. The cumulative sum method was used to calculate the recognition time of the recurrent laryngeal nerve for each patient, and the learning curve of intraoperative nerve monitoring in endoscopic thyroidectomy via sternomastoid pathway was obtained for this group of patients. The recurrent laryngeal nerve recognition time, recurrent laryngeal nerve recognition rate, incidence of recurrent laryngeal nerve injury, intraoperative blood loss, postoperative drainage volume, hospitalization time and occurrence of complications were compared at different stages of the learning curve. Results The recognition time of recurrent laryngeal nerve reached the maximum when the number of surgical cases reached 20. According to this, the curve was divided into two stages: stage A (top 20 cases) was the early learning stage, and stage B (after 20 cases) was the late proficiency stage. The recognition time of the recurrent laryngeal nerve, intraoperative blood loss, postoperative drainage volume and hospitalization time of stage B patients were shorter or less than those of stage A patients, with no statistically significant difference (all P<0.05). There were no statistically significant difference in the recurrent laryngeal nerve recognition rate, incidence of recurrent laryngeal nerve injury, and incidence of complications between stage A and stage B (all P>0.05). Conclusion The minimum number of surgical cases in which the operator could master the endoscopic thyroidectomy via sternomastoid pathway was 20. And proficient surgical operations in the later stage can shorten the recognition time and hospitalization time of the recurrent laryngeal nerve during laparoscopic thyroidectomy, reduce intraoperative bleeding and postoperative drainage volume.