Purpose: This study aimed to analyze treatment outcomes and prognostic markers, including immune and inflammatory factors, of postoperative radiation therapy (RT) administered to patients with cholangiocarcinoma (CCA).Methods: We retrospectively selected 59 patients with CCA who underwent surgery and postoperative RT with curative intent from 2004 to 2019. Patients received external irradiation (50 Gy in 25 fractions) using three-dimensional RT. Overall survival (OS), cause-specific survival (CSS), progression-free survival (PFS), and locoregional control (LRC) rates of initial RT were assessed using the Kaplan–Meier method. Univariate and multivariate Cox proportional-hazards regression models were used to identify prognostic factors. We analyzed prognostic factors of inflammation, such as pre-RT platelet count, hemoglobin, lymphocyte count ratio (LCR) of the leukocyte count, platelet-to-lymphocyte ratio (PLR), and neutrophil-to-lymphocyte ratio (NLR).Results: Tumor stages were distributed as follows: I (n = 8), II (n = 25), III (n = 15), and IVA (n = 11). The median follow-up was 24 months. Two-year OS, CSS, PFS, and LRC rates were 59.5%, 62.0%, 40.1%, and 66.7%, respectively. Univariate analysis revealed that lower LCR was significantly associated with shorter PFS (P = 0.0446, hazard ratio (HR): 1.90, 95%, confidence interval (CI): 1.02–3.58). There was no significant difference between the median baseline values of PLR and NLR; and age ≥75, positive regional lymph node metastases (N+), and chemotherapy after RT were significantly associated with poor OS. Multivariate analysis revealed a significant association of N+ with OS, PFS and CSS and that lower LCR was significantly associated with PFS (HR: 0.481, CI: 0.252–0.905, p=0.0234). Among late toxicity events, two patients (3.38%) were suspected with therapy-related liver toxicity.Conclusions: LCR before RT was a prognostic factor for postoperative radiation therapy of patients with CCA.