Background: Epstein-Barr virus-associated biliary tract cancer (EBVaBTC) has a distinct genomic landscape and increased infiltration of CD3⁺ and CD8⁺ T cells. However, the efficacy of immunotherapy in EBVaBTC remains largely unknown. The aim of this study is to assess the efficacy of programmed cell death protein 1 (PD-1) antibody in EBVaBTC. Methods: Consecutive patients with metastatic biliary tract cancer diagnosed at our institution from January 2017 to December 2021 were identified. In situ hybridization was performed to detect EBV. The objective response to PD-1 antibody was assessed. We also analyzed the immune microenvironment of EBVaBTC by multiplex immunofluorescence staining, and performed the proteomic characterization of EBVaBTC. Results: A total of 131 patients with BTC who received PD-1 antibody were identified, of which 9 (6.9%) had EBVaBTC. All EBVaBTC cases were intrahepatic cholangiocarcinoma. EBVaBTC was not associated with deficient mismatch repair but with lymphoepithelioma-like carcinoma and hepatitis B virus infection. Four (44.4%) patients achieved a partial response, and the remaining five (55.6%) patients had stable disease. The response lasted for at least 12 months in 8 (88.9%) patients with EBVaBTC, including 4 patients received PD-1 antibody monotherapy. Blood EBV-DNA was detectable in all 9 patients (100%) with EBVaBTC. Multiplex immunofluorescence staining revealed more abundant CD3⁺ and CD8⁺ T cells infiltration in EBVaBTC than that of mismatch repair deficient BTC. A total of 8,379 proteins were identified by proteomics. Comparison of EBVaBTC and paired normal tissue revealed 547 differentially expressed proteins. Enrichment analysis demonstrated that differentially expressed proteins in the EBVaBTC were associated with EBV infection and T cell activation. We also observed the expression of immune checkpoint other than PD-1, including LAG-3 and TIM-3. Conclusions: Identification of EBVaBTC may represent a subset of patients with promising response to immunotherapy.