Purpose: Although radical cystectomy (RC) and concurrent chemoradiotherapy (CCRT) are curative options for muscle-invasive bladder cancer (MIBC), the optimal treatment strategy for MIBC patients with a history of nephroureterectomy for upper tract urothelial carcinoma (UTUC) remains unclear. This retrospective analysis was conducted to compare survival rates and evaluate prognostic factors related to treatment outcomes.Materials and Methods: We conducted a multi-institutional retrospective study of patients with MIBC after nephroureterectomy for UTUC between 2005 to 2023. Out of 75 patients, 30 underwent bladder-preserving therapy (BPT), including 22 patients who underwent radiation therapy (RT) and 8 patients who underwent CCRT, while 45 patients underwent RC. The overall survival (OS), cancer-specific survival (CSS), and progression-free survival (PFS) after BPT and RC were evaluated using Kaplan-Meier curves. Cox regression analysis was used to identify variables associated with OS, CSS, and PFS. Posttreatment changes in renal function were compared.Results: At 3 years, the OS, CSS, and PFS rates in the BPT group were 52.4%, 71.7%, and 31.3%, respectively, with no significant difference compared to RC. In multivariate analysis, bladder cancer T stage was the only predictive factor for OS, CSS, and PFS. Similar results were also observed in the RT group compared to RC. A significant decrease in renal function was detected among patients in the RC group, while patients in the BPT group maintained preserved renal function. Patients in the BPT group experienced a lower grade of toxicity after treatment compared to those in the RC group, and the rates of survival with functional bladder at 1 year, 3 years, and 5 years were 87.0%, 69.9%, and 69.9%, respectively.Conclusions: Bladder-preserving therapy, including RT alone, may be a viable treatment option for patients with MIBC who have undergone nephroureterectomy, as it can achieve comparable oncologic outcomes to RC, while potentially preserving bladder and renal function.