Surgical resection is considered an effective cure for biliary tract cancer (BTC); however, the prognosis is unsatisfactory despite improved surgical techniques and perioperative management. The recurrence rate remains high even after curative resection. The efficacy of adjuvant chemotherapy in pancreatic and gastric cancers has been previously reported, and the feasibility of adjuvant therapy with S-1 has recently been reported in patients with resected BTC. We aimed to retrospectively investigate the effects of adjuvant chemotherapy with S-1 on resected advanced BTC.