Objective To investigate the efficacy of CT on diagnosis of mediastinal neoplasms and tumor-like lesion to analyze the causes of misdiagnosis. Methods Forty two patients were examined with CT, 11 patients received contrast CT scan. All cases were confirmed by pathology. Results Various mediastinal neoplasms and tumor-like lesions with heterogeneous density have their own special demonstration on CT image and frequently occurred sites. The accuracy of diagnosis before surgery is 71.4 %(30/42). Conclusions CT is useful in improving the preoperative diagnosis rate of mediastinal neoplasms or tumor-like lesions and in helping clinicians work out treatment plan.