39-year-old female had been treated for the exophytic mass on buccal aspect of the left, maxillary posterior area 2 years and 8 months ago. Tentative diagnosis was obtained as fibrous dysplasia on clinical and radiographic examinations and histopathologic findings revealed as osteochondroma after bone trimming at that time. She revisited for the treatment of recurred lesions. We reviewed this case with clinical. radiologic and histopathologic standpoints retrospectively, and came to a conclusion that the tumor primarily occurred was juxtacortical osteogenic sarcoma and recurred due to inadequate treatment and then expanded over intramedullary. This case shows that the diagnosis of osteosarcoma should take account of the patient history, clinical. radiographic and histopathologic findings and it requires attentive follow up check. Retrospectively reviewed results were as follows ; At first visit, oral examination revealed a bony hard swelling on the buccal aspect of the left maxillary posterior area. Radiographically, a dense radiopaque mass was noted on the site. The lesion showed hot uptake of ^99mTc-MDP. Histopathologic diagnosis was done as osteochondroma, but it was considered as osteogenic sarcoma when compared with the recurrent lesion. When she revisited for the treatment of multiple bony swelling on the left maxilla, radiograms showed typical features of malignancy such as widening of periodontal ligament space and sunray appearace, and coincided with benign characters as follows; relatively well circumscribed lesion and expansion and displacement of the adjacent structures. Finally, histopathologic findings of the lesion was well differentiated chondroblastic osteogenic sarcoma.