Sarcopenia accompanied by systemic inflammation is associated with poor prognosis in patients with cancer. This study evaluated the prognostic significance of sarcopenia (myopenia and myosteatosis) and systemic inflammatory markers in older patients (aged ≥80 years) with resected biliary tract cancer. Patients who underwent resection for biliary tract cancer between July 2010 and January 2023 at the NHO Fukuyama Medical Center were retrospectively reviewed. Preoperative computed tomography measured myopenia and myosteatosis, using the psoas muscle index and modified intramuscular adipose tissue content. Associations between clinicopathological characteristics, inflammation-based prognostic scores, and overall survival were analyzed using Cox proportional hazards models. Univariate analysis revealed low C-reactive protein-to-albumin ratio (<0.125), low prognostic nutritional index (<42), low modified intramuscular adipose tissue content, higher T-stage (T3-4), lymph node metastasis, and postoperative complications associated with worse overall survival in older patients (aged ≥ 80 years) with resected biliary tract cancer (n=48). Multivariate analysis identified low prognostic nutritional index (<42) (p=0.007), low modified intramuscular adipose tissue content (p=0.015), higher T-stage (T3-4) (p<0.001), lymph node metastasis (p=0.001), and postoperative complications (p=0.017) as independent predictors of overall survival. Preoperative myosteatosis and low prognostic nutritional index are independent prognostic factors for overall survival in older patients (aged ≥80 years) with resected biliary tract cancer. These factors may be useful for risk stratification and clinical decision-making. Early interventions, such as nutritional support and physical exercise, may improve outcomes after resection of biliary tract cancer.