Background/Aim: The aim of the present study was to assess clinical outcomes of postoperative radiotherapy for biliary tract cancer patients. Patients and Methods: Clinical results of 187 patients treated with external irradiation in 31 Japanese Institutions between 2000 and 2011 were retrospectively analyzed. The median radiation dose was 50.4 Gy in fractions of 1.8-2 Gy. Results: Two-year actuarial overall survival and locoregional control (LCs) rates were 56% and 68%, respectively. In multivariate analysis, macroscopic residual tumor (R2) and irradiated doses < 54 Gy were significant indicators of poor LC prognosis. For patients with complete resection (R0) or microscopic residual tumor (R1), 2-year LCs were 71% for < 54 Gy and 83% for >= 54 Gy; doses >= 54 Gy were associated with high long-term LCs. There was no significant difference in acute adverse event rates between < 54 Gy and >= 54 Gy. Conclusion: Postoperative irradiation doses of approximately 54 Gy are safe and effective for R0 or R1 resection patients.