PURPOSE: To evaluate MRI findings of malignant ovarian tumors. MATERIALS AND METHODS: MRI findings were retrospectively reviewed in 25 patients with surgically confirmed 30 malignant ovarian tumors(common epithelial tumor;23, sex cord stromal tumor;2, endodermal sinus tumor ; 1, metastatic tumor ;4). The findings evaluated were the lesion size, solid and/or cystic component, wall thickness, septal thickness, necrosis, invasion of adjacent organ, ascites, and adenopathy. RESULTS: MRI findings of the malignant ovarian tumors were as follow:Size of lesion was 5-35cm(mean 14cm) ;solid component was present in 80%(24/30);wall thickness was more than 3ram in 90%(27/30);septal thickness was more than 3ram in 70%(21/30);tumor necrosis was present in 40%(12/30%) ;invasion of adjacent organ was present in 76%(19/25);ascites was present in 56%(14/25);lymphadenopathy was present in 24% (6/25). MRI findings of absence of solid component(6/6), even wall and septal thickness(7/7, 19/19) were found only in epithelial tumors. Uneven septal thickness more than 3mm(7/11) was a predominant MRI findings of non-epithelial tumors. Well-defined cystic lesion within solid component was seen in Krukenberg tumors. CONCLUSION: Evaluation of the lesion size, internal architecture, invasion of adjacent organ, ascites, and lymphadenopathy in MRI would enable diagnosis of malignant ovarian tumors and could lead to possible differential diagnosis of epithelial tumors from non-epithelial tumors.