<b><i>Introduction:</i></b> This study had two objectives: (i) to evaluate oncological outcomes in a long-term follow-up of patients with bladder cancer after reduced-port laparoscopic radical cystectomy (RP-LRC) and (ii) to assess the effect of modified Glasgow prognostic scores (mGPS) on patient outcomes. <b><i>Methods:</i></b> Consecutive patients (<i>n</i> = 100) who received RP-LRC between March 2012 and December 2018 at our institution and affiliated hospital were retrospectively reviewed. Preoperative serum albumin and C-reactive protein levels were determined. Patients were grouped based on clinical T stage (≤cT2: <i>n</i> = 75, ≥cT3: <i>n</i> = 25) using pooled cumulative data. Oncological outcomes and mGPS as a prognostic biomarker were analyzed retrospectively. Kaplan-Meier curves displayed recurrence and survival rates. Univariate and multivariate Cox regression analyses evaluated potential prognostic factors for recurrence-free survival (RFS) and cancer-specific survival (CSS). <b><i>Results:</i></b> Patient characteristics between the two groups were statistically similar for preoperative hematological and mGPS status, blood loss level, rate of allogeneic transfusion, and pneumoperitoneum time. After a median follow-up period of 55 months, 40/100 patients experienced disease relapse. RFS and CSS for ≤cT2 were significantly less than for ≥cT3 (<i>p</i> < 0.001, <i>p</i> < 0.05, respectively). Distant metastasis occurred in 30 patients with similar distributions of relapse sites between T-stage cohorts. Median RFS for mGPS 1/2 were 18.9 (95% confidence interval [CI]: 8.8–not assessed [NA]) and 35.0 (95% CI: 8.7–NA) months, respectively, significantly worse than for mGPS 0 (median NA, 95% CI: NA–NA); CSS was similar. Univariate and multivariate analyses revealed ≥cT3 stage, worse clinical N stage, and poor mGPS status were significant prognostic factors for short RFS and CSS. <b><i>Conclusions:</i></b> A large proportion of bladder cancer patients who undergo RP-LRC experience relapse, with ≥cT3 stage, worse clinical N stage or poor mGPS status identified as significant prognostic factors. Our findings may contribute to improved surgical procedures for such patients.