Abstract Background Although the albumin-to-globulin ratio (AGR) is a promising biomarker for various malignancies, few studies have investigated its prognostic significance for upper tract urothelial carcinoma (UTUC). Methods This retrospective study conformed to the REporting recommendations for tumour MARKer prognostic studies (REMARK) guideline. We reviewed 179 patients with UTUC who underwent radical nephroureterectomy at our institution between 2008 and 2018. Associations of preoperative clinicopathological factors, including the AGR, with cancer-specific survival (CSS) and overall survival (OS) were assessed. The Cox proportional hazards model was used for univariate and multivariable analyses. AGR was dichotomized as < 1.25 and ≥ 1.25, according to the most discriminatory cutoff determined from the receiver operating characteristic curve analysis. Results During a median follow-up of 34 months after surgery, 37 patients died from UTUC and 13 died of other causes. The preoperative AGR significantly correlated with pathological T stage, pathological N stage, and adjuvant chemotherapy. Multivariate analyses demonstrated that a decreased (< 1.25) preoperative AGR was an independent poor prognostic factor for both CSS (hazard ratio [HR] = 2.81, P < 0.01) and OS (HR = 2.09, P < 0.05). Conclusions Preoperative AGR < 1.25 might serve as a useful prognostic marker for patients with UTUC undergoing radical nephroureterectomy.