Abstract:For patients with unresectable malignant biliary obstruction due to cholangiocarcinoma, endoscopic or percutaneous biliary drainage represents the main palliative treatment. Previously, photodynamic therapy (PDT) for malignant biliary tumors via endoscopic retrograde cholangiopancreatography or percutaneous transhepatic approach under fluoroscopic guidance, combined with biliary stent implantation, has been shown to help prolong patient survival and improve quality of life. However, this strategy is limited by the inability to achieve precise targeted irradiation of the lesions.Herein, we report a case of a 67-year-old male patient with poorly differentiated adenocarcinoma of the common bile duct who underwent PDT under direct visualization using a peroral cholangioscope, enabling accurate localization and targeted irradiation of the lesion under endoscopic guidance.