Primary leiomyosarcoma in the lung is extremly rare tumor.It can appear as either an intrabronchial or a parenchymal lesion, and may arise in the pulmonary artery or its branches. It resembles carcinoma of bronchus in its symtomatology, physical signs and radiology, but leiomyosarcoma occurs in patients who are average of two decades younger than those with bronchogenic carcinoma, and metastasis to the lymphnode is unusual. So histologic examination is reliable in diagnosis and differentiation from carcinoma. We have experienced one case of primary leiomyosarcoma in the left lower lung. A brief review of literature was done.