Abstract： Biliary tract cancer is a group of malignancies that originate in the biliary epithelium, and adenocarcinoma is the main pathological type. Although surgical resection is the only radical treatment strategy, most patients with biliary tract cancer are diagnosed at a locally advanced stage or with distant metastases. Biliary tract cancer is highly resistant to conventional chemoradiotherapy and emerging immunotherapy including immune checkpoint inhibitors, due to the suppressive immune microenvironment. In general, this paper discussed the anti-tumor and tumor-promoting immune responses of various immune cells and stromal cells in the immune microenvironment of biliary tract cancer, as well as their correlation with prognosis. Understanding the whole view of the immune microenvironment in patients with biliary tract cancer could further inform the design of clinical trials of immunotherapy or combination therapy.