Undifferentiated pleomorphic sarcoma (UPS) was previously known as malignant fibrous histiocytoma (MFH). This sarcoma occurs preferentially in the extremities and retroperitoneal space; primary pulmonary UPS/MFH is rare. We report a 52-year-old woman referred to our hospital with dyspnea and severe cough. Chest computed tomography (CT) revealed a pulmonary mass in the left upper lobe and pleural effusion. Cytology of the effusion showed no malignancy; however, the tumor increased rapidly in size, and the patient's respiratory symptoms worsened. The tumor occupied almost all of the left upper lobe and involved the adjacent pericardium. She underwent left upper lobectomy with pericardial resection and reconstruction. Postoperative pathology of the resected specimen showed undifferentiated pulmonary sarcoma, pT4N0M1a stage IV A, and genetic analyses revealed the v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation. The patient's dyspnea recurred 1 month postoperatively, and CT showed marked pleural effusion. An 18F-fluorodeoxyglucose positron emission tomography demonstrated abnormal diffuse accumulation of 18F-fluorodeoxyglucose in the left pleural cavity. We initiated five cycles of chemotherapy with doxorubicin and ifosfamide, and the patient has been well without recurrence for 24 months after multidisciplinary treatment with surgery followed by systemic combination chemotherapy. We successfully treated our patient with primary pulmonary UPS/MFH using a multidisciplinary approach, even though this sarcoma carries a poor prognosis and is insensitive to both chemotherapy and radiotherapy.