Objective:To analyze the risk factors of biliary infection after endoscopic retrograde cholangiopancreatography (ERCP) in patients with malignant biliary obstruction.Methods:Clinical data of 160 patients with malignant biliary obstruction admitted to the Affiliated People's Hospital of Ningbo Univer-sity from June 2017 to June 2022 were retrospectively analyzed, including 89 males and 71 females, aged (65.1±8.0) (range, 41-78) years old. Patients were divided into two groups according to the occurrence of biliary infection within 30 days after ERCP: infected group ( n=30) and uninfected group ( n=130). Multivariate logistic regression was used to identify the risk factors of postoperative biliary infection. Results:The incidence of biliary infection after ERCP was 18.8% (30/160) in the patients with malignant biliary obstruction. A total of 43 strains of pathogenic bacteria were detected, including 34 Gram-negative strains and nine Gram-positive strains. The most common pathogenic bacterium was Escherichia coli. Multivariate analysis showed patients with diabetes mellitus ( OR=2.356, 95% CI: 1.587-5.441, P=0.001), sphincter dysfunction ( OR=2.651, 95% CI: 1.854-6.225, P=0.005), preoperative albumin <35 g/L ( OR=3.225, 95% CI: 2.041-5.689, P=0.002), preoperative hemoglobin <110 g/L ( OR=3.424, 95% CI: 2.115-6.333, P=0.003) suffered a higher risk of biliary infection after ERCP. Conclusion:Diabetes mellitus, sphincter dysfunction, lower levels of preoperative albumin and hemoglobin are independent risk factors for biliary infection after ERCP in patients with malignant biliary obstruction.