Objective To discuss the clinical value of systemic immune-inflammation index(SII)in predicting the prognosis of patients with extrahepatic cholangiocarcinoma(ECCA)treated with biliary stenting combined with 125I seeds implantation.Methods A total of 128 patients with unresectable ECCA,who received biliary stenting combined with 125I seeds implantation at the Interventional Department of the Affiliated Hospital of Xuzhou Medical University of China between August 2018 and August 2021,were enrolled in this study.The peripheral blood routine testing was performed within 3 days before operation,based on which the SII was calculated.Receiver operating characteristic(ROC)curve was applied to determine the optimal cut-off value of SII,based on which the patients were divided into high-SII group and low-SII group.Cox regression model was used to analyze the independent factors affecting patient prognosis.The Kaplan-Meier curve was plotted to analyze the one-year survival.Results The optimal cut-off value of SII was 1 050,the sensitivity was 66.0％,the specificity was 69.3％,and the area under ROC curve of SII was 0.676.The one-year survival rate of patients with ECCA in the high-SII group was significantly lower than that in the low-SII group(P＜0.05).Univariate Cox regression analysis indicated that vascular invasion,T stage,adjuvant chemotherapy,CA19-9,and preoperative SII were the important factors affecting the prognosis of patients with ECCA.Multivariate Cox regression analysis revealed that T stage,CA19-9,and preoperative SII were the independent risk factors for patient prognosis,while adjuvant chemotherapy was a protective factor.The Kaplan-Meier curves showed that the one-year survival rate in high-SII group was remarkably lower than that in the low-SII group.Conclusion Preoperative SII has an important value in evaluating the prognosis of patients with ECCA who are treated with biliary stenting combined with 125I seed implantation.(J Intervent Radiol,2023,32:1221-1225)