Objective:To explore the clinical value of X-ray and CT in detecting unusual mediastinal mass.Methods:The chest plain films and CT scans were performed in all 9 cases .Results:Nine cases proved by operation and pathology included liposarcoma(two cases),multiple neurinoma(two cases),neuroendovrine cartinoma(two cases),endodermal sinus tumor(two cases)and thymas cacinoid (one case).Conclusion:X-ray and CT can localze the mediastinal mass,CT has more significance in detecting the internal morphology of mediastinal mass and its relationship with the surrounding tissues.But there is still a limitation for X-ray and CT in detecting the quality of some mediastinal carcinomas.