Primary pulmonary artery sarcoma is an uncommon tumor. Mandelstamm in 1923 was the first to describe the disease in an autopsy. Since then, less than 200 cases were reported. The incidence is 0.001-0.03%, they are always highly malignant sarcoma, and women are involved twice as often as men. The presentation is often cough, dyspnea, and chest pain, and patients are usually diagnosed as suffering from pulmonary emboli, and primary tumor of the pulmonary artery is not usually considered in the differential diagnosis. The diagnosis of pulmonary artery sarcoma is made of the "clot" resected during pulmonary artery thrombendarterectomy. Our suggestion is that in patients with unilateral pulmonary artery occlusive disease, no evidence of positive hypercoagulability tests, and no history of thromboembolism, a high suspicion of pulmonary artery sarcoma should be kept in mind, and an angiographic-guided biopsy from the intra-arterial occlusive material should be considered. The treatment is surgery. The survival without operation is less than 2 months. Some patients were treated with adjuvant chemotherapy. We report on a woman with undifferentiated sarcoma of the pulmonary artery, mimicking chronic pulmonary artery emboli. This case illustrates the need to consider malignancy in the differential diagnosis of patients having pulmonary emboli.