Low skeletal muscle mass is frequently observed in cancer patients and is known to be a poor prognostic factor for survival outcomes. The purposes of our study were to determine the prevalence of sarcopenia and its relation to mortality in biliary tract cancer. Body composition measurements (skeletal muscle index, total fat mass, bone mineral content) were evaluated by using dual-energy x-ray absorptiometry in 75 biliary tract cancer patients before chemotherapy. Muscle strength was measured by handgrip strength and gait speed. Overall survival and its associated factors were determined. The mean appendicular muscle mass was 17.8±2.7 kg in men and 14.0±2.1 kg in women (p < 0.05). Sarcopenia was diagnosed in 46 patients (61.3%) and higher proportion of men was classified as sarcopenia than women (69.0% vs 35.3%, p < 0.05). Multivariable analysis adjusted for chemotherapy regimen and age revealed that high appendicular muscle mass independently predicted better survival outcomes (HR 0.40; 95% CI, 0.18 to 0.88; p = 0.023). Sarcopenia is common in biliary tract cancer patients and low appendicular muscle mass was associated with poor survival outcome.