There is relatively little literature on adjuvant radiotherapy after radical nephroureterectomy with bladder cuff excision (RNU) for patients with upper tract urothelial carcinoma (UTUC). This study was designed to determine the efficacy of adjuvant radiotherapy for patients with pT3N0M0 UTUC. We retrospectively reviewed 198 patients treated with RNU between December 2001 and January 2015. Postoperative radiotherapy was administered in 40 (20.2%) of patients. Patients who received radiotherapy were younger than those that did not (65.2 vs. 70.5 years, p = 0.023). With median follow up of 29.1 months, Kaplan-Meier analysis with the log-rank test demonstrated no significant differences between those omitting vs receiving adjuvant radiotherapy in regards to 2-year rates of overall survival (72.0% vs. 73.4%, p = 0.979), cancer-specific survival (73.2% vs. 75.3%, p = 0.844), and recurrence-free survival (61.2% vs. 66.3%, p = 0.742). However, in multivariable analysis with Cox regression, young age, absence of chronic kidney disease, negative lymphovascular invasion, negative surgical margin, and adjuvant chemotherapy were also associated with better cancer-specific survival. In conclusion, adjuvant radiotherapy did not offer any significant benefit in terms of overall, cancer-specific, and recurrence-free survivals in patients with pT3N0M0 UTUC after RNU. More effective systemic adjuvant chemotherapy is necessary to improve the outcome of these patients.