Objective To explore MRI features of struma ovarii (SO)and analyze the causes of misdiagnosis.Methods The MRI data of 5 patients with SO confirmed by surgery and pathology were analyzed retrospectively.Results The MRI features of SO were summarized as follows:(1)The lesions were often unilateral.(2)The maximal diameter was 3.6-13 cm and the volume was 37.8-854.1 cm3 .(3)The irregular shape was presented in 2 cases,round shape was presented in 2 cases,and superficial lobulated shape was presented in 1 case.(4)The boundary of the lesions was clear,and the adjacent organs were compressed without obvious inva-sion,there was 1 patient showing moderate ascites.(5 )The tumor was cystic or solid-cystic with various size,and capsular space showed homogeneous high,equal or low signal intensity on T1 WI and T2 WI.Irregular solid component and thick separation were be-tween capsular spaces.The wall,solid component,and separation showed significant contrast-enhancement.Conclusion Recognition of the MRI features of SO could improve the diagnostic accuracy and avoid misdiagnosis.