Background: Biliary tract cancer (BTC) is a relatively uncommon but highly fatal malignancy and most patients with BTC are diagnosed at advanced stages. Currently, no standard second-line treatment has been established following recurrence from the first-line treatment. VEGF is highly expressed in more than 50% of BTC, which indicates anti-angiogenesis might be a potentially effective method to improve the outcome in BTC. Fruquintinib is a novel small molecule tyrosine kinase inhibitor targeting VEGFR1, VEGFR2, and VEGFR3 and is currently being evaluated in clinical trials for multiple cancers including lung cancer, gastric cancer and colorectal cancer, and showed strong anti-tumor activity. However, the effect and safety of fruquintinib has not been investigated in the setting of second-line treatment for BTC. Methods: The study is a multicenter, single-arm, phase 2 trial of fruquintinib (5 mg, po, for 3 weeks, followed by 1 week off, 4 weeks for a cycle) for patients with advanced or metastatic BTC who have failed to first-line chemotherapy. The primary endpoint is progression-free survival (PFS) with the null hypotheses of 8 weeks, and the median PFS≥15 weeks as evidence of the study drug activity (α=0.05, 80% power, one-sided). The number of patients required to complete the study is 27. Allowing for 20% expulsion rate, the study needs 33 patients. The secondary endpoints include objective response rate (ORR), disease control rate (DCR), overall survival (OS), safety and quality of life (QoL). Meanwhile, the study also set an exploratory objective to evaluate the mutation status of related genes in plasma (cfDNA) and tumor tissue and explore the interplay between mutation patterns with efficacy. Major eligibility requirements: Age ≥18 years; Histologically or cytologically confirmed diagnosis of advanced or metastatic biliary tract adenocarcinoma; First-line chemotherapy failed (tumor progression or intolerable adverse events); No less than 3 months of expected survival; ECOG PS≤1; At least one measurable lesion according to RECIST 1.1 criteria; Adequate organ function. Eligible patients with advanced or metastatic BTC refractory to first-line chemotherapy will be enrolled at 7 medical centers in China. The study is open and actively enrolling at time of submission. Clinical trial information: NCT04156958.