Leiomyosarcoma is a malignant soft tissue tumor predominantly affecting the uterine and gastrointestinal tract. Primary pulmonary leiomyosarcoma is very rare. It is diagnosed only after other primary origins have been excluded. Less than 100 cases have been reported worldwide in the literature. Most of the reported cases involved a unilateral lung, and only a few cases had bilateral lung involvement on diagnosis. We herein report a case of pulmonary leiomyosarcoma with bilateral lung involvement and no other detectable primary origin. Although the patient had a good performance status initially, the poor prognosis was inevitable in this unresectable condition. Palliative chemotherapy was given. Ultimately, the patient succumbed to the disease.