Objective To explore the biliary tract microbiota changes before and after drainage treatment in patients with malignant biliary obstruction(MBO),and to study the effects of biliary obstruction and drainage intervention on the bile microbiota from a microecological point of view.Methods From January 2020 to December 2022,DSA-guided percutaneous transhepatic catheter drainage(PTCD)was carried out in 32 patients with MBO.A 22G drainage needle was inserted into the bile duct,and about 15-20mL of bile was extracted after it was confirmed that the needle was located within the intrahepatic bile duct,then,an external drainage tube,or an internal drainage tube together with an external drainage tube,was implanted into the bile duct along the guide wire.Seven days after PTCD,bile was extracted through a drainage tube.Bile sampling for germiculture and gene sequencing was conducted twice.The general data of patients,including whether acute cholangitis occurred and its severity,whether antibiotics was used for treatment,etc.,were collected.Results Of the 32 patients,cholangiocarcinoma was seen in 15,pancreatic cancer in 10,hepatocellular carcinoma in 3,and hilar lymph node metastasis from gastrointestinal malignant tumor in 4.Before PTCD,in the bile microbiota the burkholderia,acinetobacter,pseudomonas and staphylococcus were the bacteria with a high relative abundance,and the diversity and evenness of other microbial species seen in the normal biliary tract were reduced.Conclusion There is a stable microbiota within the normal biliary system,and in malignant obstructive biliary tract the microbiota has similar composition.After biliary drainage,the abundance of intestinal flora in bile is increased,and the species richness and diversity of the original biliary tract microbial community are decreased,which may explain the clinical phenomenon that patients are more prone to biliary tract infection after biliary drainage.(J Intervent Radiol,2024,33:516-522)