Cholangiocarcinoma is a rare primary liver cancer with poor prognosis, due to the advanced stage at the time of diagnosis and limited therapeutic options, with poor response. Chemotherapy remains the standard first-line treatment, but the advent of immunotherapy has recently induced promising results. Given the fact that diagnosis frequency is increasing nowadays and the survival rate remains very low, it is crucial to recognize patients who are suitable for immunotherapy and will have the best response. Different types of biomarkers, such as interleukins, exosomes, mi-RNA, ctDNA, and gene mutations, have been studied for their feasibility, not only for the early diagnosis of biliary tract cancer but also for the determination of responsiveness in treatment. Less frequently, these studies focus on finding and observing biomarkers in patients who receive immunotherapy. This review aims to summarize current knowledge of existing/promising biomarkers in patients with unresectable or metastatic cholangiocarcinoma, treated with immunotherapy as monotherapy, or combined with chemotherapy.