Mediastinal masses represent a vast, group of tumors and pseudo– tumors this work evaluate of MRI in the diagnosis of pediatric patients with malignant lesions. This study was conducted on so patients; 28 males and 22 females, shown to have different lesions by chest X-ray and CT. They underwent MRI with T1 and T2 weighted fast spin echo sequences. In conclusion for our studied cases the total MRI accuracy = 92%, sensitivity = 92.3% and specificity = 100%