A 68-year-old female was admitted to our hospital for further examination of abnormal shadow on chest X-ray. Needle biopsy could not establish pathological diagnosis. Three years later, chest computed tomography (CT) revealed the tumor was enlarged. We suspected it was a malignant tumor, and resected by video-assisted thoracoscopy. The tumor occurred from the right middle lobe, and intraoperative diagnosis was malignant tumor. We added middle lobectomy. Histological examination revealed that tumor was malignant solitary fibrous tumor.