BACKGROUND: High subcutaneous adipose tissue radiodensity (SATr), an indirect surrogate marker of adipose tissue quality, was associated with poor prognosis in various cancers. The present study aimed to assess the association of SATr with survival outcomes in patients with advanced biliary tract cancer (BTC). METHODS: This retrospective, single-center study included patients with unresectable or recurrent BTC who underwent chemotherapy/chemoradiotherapy. Overall survival (OS) and progression-free survival (PFS) were assessed using the log-rank test and the Cox proportional hazards model according to the SATr status. RESULTS: The study cohort included 234 patients, including 38 and 196 patients with high and non-high SATr, respectively. The median OS durations were 10.5 and 17.4 months (HR = 1.72, 95% CI: 1.19-2.49, p < .01) and the median PFS durations were 4.9 and 8.0 months (HR = 1.52, 95% CI: 1.05-2.20, p = .03) in patients with high and non-high SATr, respectively. By multivariate analysis, high SATr, neutrophil/lymphocyte ratio >5, modified Glasgow prognostic score 1-2, and serum carcinoembryonic antigen >5.0 ng/mL were predictors for OS (HR, 1.66, 2.42, 2.00, and 1.56, respectively; p < .05). By multivariate analysis, metastatic disease status, high SATr, neutrophil/lymphocyte ratio >5, and modified Glasgow prognostic score 1-2 were independent risk factors for worse PFS (HR, 1.56, 1.56, 1.81, and 1.57, respectively; p < .05). CONCLUSIONS: High SATr was associated with risk of tumor progression and poor prognosis in patients with advanced BTC treated by palliative chemotherapy/chemoradiotherapy.