We reported a case of 66-year-old female with leiomyosarcoma of the right lower lobe of the lung with the complaint of abnormal shadow of the chest roentgenogram. On December 2, 1987, partial resection was performed and the tumor was totally removed. Histological examination revealed primary leiomyosarcoma of the lung. By electron microscopic observation, pinocytotic vesicle was not observed, but myofilaments were observed in the cytoplasm.