488 Background: We have previously reported that GEMOX combined with lenvatinib and PD-1 antibody (GOLP regimen) showed promising efficacy as first-line treatment for advanced intrahepatic cholangiocarcinoma (iCCA), indicating that GOLP regimen may be an ideal conversion therapy for patients (pts) with potentially resectable advanced biliary tract cancer (BTC). This phase II trial explored the efficacy and safety of GOLP as conversion therapy in potentially resectable and locally advanced BTC. Methods: Patients with potentially resectable locally advanced BTC were enrolled and received tislelizumab (200mg, Q3W) and lenvatinib (8mg, QD) and GEMOX chemotherapy (Q3W) including gemcitabine 1000mg/m2 on day 1, 8 and oxaliplatin 85mg/m2 on day 1. Tumor responses were evaluated every 9 weeks according to RECIST v1.1, and the resectability was simultaneously discussed by MDT. For pts who were eligible for surgery, capecitabine alone was administered as adjuvant therapy after radical surgery. Pts who was not suitable for surgery continued to the original treatment regimen until progression or intolerable toxicity. The primary endpoint was R0 resection rate, and secondary endpoints included ORR, DCR, PFS, OS, CPR, MPR, RFS. Results: From December 2021 to July 2023, 41 pts were enrolled, 21 males and 20 females with a mean age of 57 years. 87.8% pts had iCCA, 7.3% had perihilar bile duct cancer and 4.9% had gallbladder cancer. TNM stage was II, IIIA, IIIB and IIIC for 2.4%, 34.1%, 58.5% and 4.9% of pts respectively. At cut-off date (September 10, 2023), the mean follow-up was 7.7 months, 39 pts completed at least three cycles of conversion therapy and 7 pts still administered with scheduled conversion therapy. The ORR was 43.9% (18/41) and the DCR was 87.8% (36/41). The median duration of therapy before surgery was 2.9 months (95%CI 2.6-4.6), R0 resection rate was 48.8% (20/41), and 2 pts underwent R1 resection. 9.1% (2/22) pts had a pCR and 22.7% (5/22) had an MPR. The most common grade 3/4 treatment-related adverse events (TRAEs) included neutropenia (31.7%), increased GGT (19.5%), leukopenia (12.2%). No grade 5 AEs occurred. Conclusions: This study demonstrates the high effectiveness and manageable safety of GOLP regimen as conversion therapy for potentially resectable locally advanced BTC. Survival data will continue to be followed up. Clinical trial information: NCT05156788 .