Background: Despite that PD-1/L1 inhibitors combined with chemotherapy have been approved as first-line(1L) treatment for advanced biliary tract cancer (BTC), the overall survival benefit remains limited, particularly for patients with gallbladder cancer. Ivonescimab, a tetrameric bispecific antibody targeting PD-1 and VEGF, has the potential to produce complementary and synergistic anti-tumor effects through both pathways. This study aimed to evaluate the safety and efficacy of ivonescimab in combination with chemotherapy in advanced BTC. Methods: This was an open-label, multi-center phase II study in patients with unresectable locally advanced and metastatic BTC. Ivonescimab was administered every 3 weeks for up to 8 cycles, along with gemcitabine and cis-platinum. After that, ivonescimab monotherapy was given until disease progression or unacceptable toxicity. The primary endpoints were safety and objective response rate (ORR) by RECIST v1.1. Secondary endpoints included duration of response (DoR), disease control rate (DCR), time-to-response (TTR), progression-free survival (PFS), and overall survival (OS). Results: As of Nov 26, 2023, a total of 22 pts with advanced BTC were enrolled in the study. The median age was 65.0 years (range, 47-75), 81.8% of patients had ECOG of 1. All patients had initially unresectable disease status, 54.5% of patients had intrahepatic cholangiocarcinoma, 4.5% of patients had extrahepatic cholangiocarcinoma and 40.9% of patients had gallbladder cancer at baseline. The median follow-up time was 10.7 months, and the median exposure time of ivonescimab was 7.2 months. A total of 86.4% (19/22) of patients experienced at least one grade 3 or higher treatment-related adverse event (TRAE), but none led to discontinuation treatment or death. The most common grade 3/4 TRAEs with a frequency of at least 10% included white blood cell count decreased (50.0%), neutrophil count decreased (50.0%), anemia (40.9%), platelet count decreased (22.7%), and hypertension (13.6%). The ORR by investigator assessment was 63.6% (14/22) regardless of PD-L1 status, with an ORR of 77.8% (7/9) for gallbladder cancer patients specifically. The DCR was 100% (22/22). The median PFS was 8.5 months (95% CI, 6.8-9.9), with a 6-month PFS rate of 84.2% (95% CI, 58.7-94.6). The median OS was 16.8 months (95% CI, 9.8- NE), with a 9-month OS rate of 81.8% (95% CI, 58.5-92.8). Conclusions: Ivonescimab combined with chemotherapy as 1L treatment demonstrated promising efficacy in pts with advanced BTC. Further trials to validate the efficacy and safety are warranted. Clinical trial information: NCT05214482.