BACKGROUND: Primary pulmonary artery sarcomas are very rare and their histologic type called leiomyosarcoma is even rarer. These tumors are frequently misdiagnosed as pulmonary thromboembolism in clinical settings. Many patients receive anticoagulant therapy without response, and many are diagnosed postmortem only. Most of the tumors reported in the literature have involved the right ventricular outflow tract and the main pulmonary trunk, often extending into the main pulmonary artery (MPA) branches. CASE REPORT: A 64-year-old woman presented with weakness, fatigue, malaise, dyspnea, and marked elevation of pulmonary artery pressure was admitted to our hospital. She was initially diagnosed with chronic pulmonary thromboembolism, and chest computed tomography (CT) scan revealed lobulated heterogeneous left hilar mass extended to precarinal and subcarinal space. Magnetic resonance imaging (MRI) demonstrated a polypoid lesion at the trunk with extension to left MPA and its first branch. The patient was operated, and a yellowish-shiny solid mass in pulmonary trunk was seen intra-operation and pulmonary endarterectomy was performed. Her tumor was pathologically diagnosed as pulmonary artery leiomyosarcoma. CONCLUSION: Clinicians must consider pulmonary artery sarcoma when making the differential diagnosis for patients with pulmonary artery masses. The clinical prediction scores and the CT and MRI findings can help identifying patients with pulmonary artery sarcoma.   Keywords: Hypertension, Leiomyosarcoma, Pulmonary Artery, Pulmonary Embolism