【Abstract】 Objective To evaluate the characteristics of the invasion of portal vein in patients with hilar cholangiocarcinoma on magnetic resonance imaging (MRI), the anatomic distribution of portal vein involved and its correlation with BismuthCodett classification.Methods 40 inpatients with biopsyconfirmed hilar cholangiocarcinoma between January 2014 and October 2016 were enrolled into this study. All patients underwent routine MRI scans, magnetic resonance cholangiopancreatography and threedimensional volume of the ultrafast multiphase dynamic contrastenhanced scans (3D CE LAVA).On MRI, presence or absence and signs of the portal vein invasion, and its anatomic distribution were reviewed, and the correlation of the invasion of portal vein by hilar cholangiocarcinoma with BismuthCodett classification was assessed.Results The incidence of the invasion of portal vein by hilar cholangiocarcinoma was 82.5% (33/40). The main characteristics were embedded, compression, narrowing or occlusion of portal vein including 5 patients with tumor thrombus in the portal vein, 14 patients with broadened portal vein, 4 with broadened splenic vein and 5 with splenomegaly. The left branch, the right branch of portal vein invasion occurred in 12 and 6 cases, respectively. The main portal vein was involved in 2 cases, and the involvement of the main portal vein and its left and right branches or that of any two of the previous veins occurred in 13 cases. The type Ⅲ and Ⅳ of hilar cholangiocarcinoma were more likely to invade the portal vein than typeⅠand Ⅱ(P＜0.05).Conclusion MRI can accurately show the status of portal vein invasion by hilar cholangiocarcinoma, which can be helpful for the treatment decision making.