The aim of this study was to investigate the prognostic role of blood-based nutritional biomarkers, including red blood cell (RBC count), hemoglobin (Hb), total protein (TP), albumin, the serum albumin to globulin ratio (AGR) and the prognostic nutritional index (PNI) in patients who underwent intravesical treatment for non-muscle invasive bladder cancer (NMIBC). A total of 501 NMIBC patients who received intravesical Bacillus Calmette-Guerin (BCG) treatment following transurethral resection of bladder tumor (TURBT) were included. The optimal cutoff values for these nutrition-based indicators were determined using receiver operating characteristic curve analysis. We observed a significantly higher recurrence-free survival (RFS) rate in patients with elevated levels of RBC count, Hb, TP, and albumin. Cox univariate and multivariate Cox regression analyses demonstrated that serum albumin (P = 0.002, HR = 0.51, 95%CI: 0.33-0.78), RBC count (P = 0.002, HR = 0.50, 95%CI: 0.32-0.77), TP (P = 0.028, HR = 0.62, 95%CI: 0.41-0.95), Hb (P = 0.004, HR = 0.53, 95%CI: 0.33-0.84), AGR (P = 0.003, HR = 0.46, 95%CI: 0.27-0.76) and PNI (P = 0.019, HR = 0.56, 95%CI: 0.35-0.91) were significant independent factors predicting RFS. These cost-effective and convenient blood-based nutritional biomarkers have the potential to serve as valuable prognostic indicators for predicting recurrence in NMIBC patients undergoing BCG-immunotherapy.© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.