The leiomyosarcoma is uncommon tumor that consists of 10% of all sarcoma incidence and commonly arise from retroperitoneum or mesentery. But leiomyosarcoma arose from mediastinum is very rare and only incidental case report is present. Mediastinal leiomyosarcoma may originate from superior vena cava, pulmonary artery, small vessels of alveoli, esophagus and cardiac muscle. Common symptoms that are related with leiomyosarcoma of mediastinum are cough and dyspnea but dysphagia, chest pain and hemoptysis can be produced. Although long term survival after complete resection of tumor was reported in localized disease, there was no effective therapy that prolong the survival in patients who had disseminated disease or huge tumor mass. We report the case of posterior mediastinal leiomyosarcoma confirmed by aspiration cytology and immunohistochemical staining, along with a review of literature.