An abnormal shadow was detected in a 75-year-old man on a chest roentgenogram, and the patient was referred to our institution. A transbronchial biopsy was carried out and the specimen resulted in a diagnosis of organizing pneumonia. During the follow-up period, the left lung lesion became enlarged. Partial resection of the left lung was performed. Postoperatively, pathological examination of the tumor showed an organizing pneumonia. Approximately 3 years later, a new calcified heterogeneous mass shadow was detected in the left lung and left pleura, which had gradually enlarged. Computed tomography (CT)-guided fine-needle biopsy of the nodule of the left pleura was performed. Microscopically, the specimen led to the diagnosis of low-grade osteosarcoma. Re-evaluation of the primary and secondary lesions were confirmed as the same histopathological findings. A further systemic examination was performed. Finally, the lesion was confirmed as low-grade osteosarcoma of the lung. The patient refused further treatment and died due to respiratory failure.