Primary pulmonary artery leiomyosarcoma is a rare tumor that can be misdiagnosed as acute or chronic pulmonary thromboembolic disease. In this report, we present a case of a 58-year-old woman initially diagnosed with chronic thromboembolic pulmonary disease, but who was later found to have pulmonary artery leiomyosarcoma. A complete mass resection was performed surgically. The definitive pathologic examination was consistent with pulmonary artery leiomyosarcoma. Although the patient did not receive adjuvant therapy after the surgery, she had a good outcome and was free of disease 8 months after surgery.