Endobiliary radiofrequency ablation (RFA) with biliary stent has been reported to be a beneficial treatment option for palliation of malignant biliary strictures. RFA uses a high-frequency alternating current to generate heat and achieve coagulative necrosis when in contact with tissue. Within the bile duct, RFA appears to be safe and may result in decreased tumor ingrowth. However, most of therapeutic effects were expected to delay bile duct obstruction rather than to decrease the tumor. Recently orally available chemotherapeutic agent, S-1, an oral fluoropyrimidine, was reported as effective in patients with bile duct adenocarcinoma. To date, little is known about the role of the addition of systemic chemotherapy to RFA for cholangiocarcinoma. The aim of this study is to evaluate the combined effect of RFA and S-1 in patients with unresectable cholangiocarcinoma.