This study aimed to evaluate the value of lymph node (LN) number as a predictor for adjuvant treatment in node-positive endometrial cancer. Data of 441 patients diagnosed with International Federation of Gynaecology and Obstetrics (FIGO) stage IIIC endometrial cancer and who underwent adjuvant chemotherapy alone or chemoradiotherapy between 2009 and 2015 from the Taiwan Cancer Registry were reviewed. The patients were stratified based on the number of positive LN as follows: 1, 2–5, and ≥ 6. The overall survival (OS) was analysed using the Kaplan–Meier method and the Cox proportional hazards model. In multivariable analysis, chemoradiotherapy was independently associated with improved OS (hazard ratio [HR]: 0.62, 95% confidence interval [CI]: 0.43–0.90; p = 0.01) compared with chemotherapy alone. Patients with ≥ 6 positive LNs were associated with a worse OS (HR: 2.22, 95% CI: 1.25–3.95; p = 0.006) and those with 2–5 LNs were not associated with a worse OS (HR: 1.56, 95% CI: 0.94–2.59; p = 0.09) compared to patients with one LN. When stratified based on LN number, chemoradiotherapy was found to significantly improve the 5-year OS of patients with ≥ 6 positive LNs compared to chemotherapy alone (35.9% vs. 70.0%, p < 0.001). No significant differences between chemotherapy alone and chemoradiotherapy were observed in 5-year OS among patients with one LN (73.1% vs. 80.8%, p = 0.31) or 2–5 positive LNs (71.4% vs. 75.7%, p = 0.68). Lymph node number may be used to identify node-positive endometrial cancer patients who are likely to have improved OS with intensification of adjuvant therapy.