A 66-year-old man was admitted to our hospital because of induction therapy of interferon for chronic hepatitis due to hepatitis C virus. On routine investigation, a mass-like lesion was detected at the level of the hilum of the left lung on the chest plain radiograph. On the thoracic CT, the heterogeneous tumor, including calcification, was 6 cm in diameter in the posterior mediastinal area, and the rib and vertebra had been damaged by it. The tumor extended to the descending aorta and the left main bronchus. A small nodule in the left S1 + 2 was noted on another slice section of this thoracic CT. The possible diagnoses, based on these radiological findings, for this tumor were primary lung cancer, posterior mediastinal tumor and malignant tumor originating from the chest wall. The diagnosis of chondrosarcoma was made based on the histological findings of the specimen obtained from the tumor. This tumor could not be resected in this case, because it had extensively damaged the rib and vertebra, and the nodular lesion in the left S1 + 2 was regarded as a metastasis from it. Although reports of chondrosarcoma originating from a rib and presenting as a posterior mediastinal tumor-like shadow are rare, chondrosarcoma should be considered as a possible diagnosis for such tumors-posterior mediastinal masses with characteristic findings such as a large tumor in contact with the chest wall, and containing calcification, with destruction of bone and dissection of the rib as shown in our CT findings.