Inflammatory myofibroblastic tumors are lesions that usually affect young adults and children. Numerous extrapulmonary sites of these tumors have been found, but the mesentery is a very unusual location for an inflammatory myofibroblastic tumor and it is extremely rare in an older patient. Inflammatory myofibroblastic tumor of the mesentery is often demonstrated as a large and infiltrative lesion with heterogeneous enhancement. Its diagnosis is recognized as difficult and it often mimics malignant tumor. We report a case of mesenteric inflammatory myofibroblastic tumor mimicking a necrotized malignant mass in a 55-year-old man who was examined with magnetic resonance imaging. To our knowledge, this is the first report of magnetic resonance imaging of mesenteric inflammatory myofibroblastic tumor with extensive central necrosis in an older patient.