The purpose of this study was to determine the prognostic value of the Geriatric Nutritional Risk Index (GNRI) in patients with upper tract urothelial carcinoma (UTUC) after radical nephrectomy (RNU). A retrospective study of UTUC patients was conducted at West China Hospital between May 2016 and June 2019. The optimal cut-off point for GNRI was determined using the X-Tile procedure. Univariate and multivariate analyses were performed to identify predictors, and two- and four-year cancer-specific survival (CSS) prediction nomograms were created based on the results of the multivariate analyses. Furthermore, time-dependent ROC curve, calibration curve and decision curve analyses were conducted. A total of 219 patients with UTUC following RNU were identified and subsequently divided into three groups based on the critical values of GNRI (91.2, 98.8). GNRI was identified as a significant risk factor for CSS, with patients exhibiting higher GNRI demonstrating elevated CSS (hazard ratio = 0.58; 95% confidence interval, 0.32-0.92; P = 0.037). Furthermore, the GNRI-based nomogram demonstrated high predictive capacity for CSS, with areas under the curve of 0.810 and 0.842 for 2- and 4-year CSS, respectively. Preoperative GNRI is an independent predictor for CSS in UTUC patients who underwent RNU and should be considered as a promising personalized tool for clinical decision-making.© 2025. The Author(s).