Osteosarcoma is a classical malignant bone-forming neoplasm which usually presents with an aggressive clinical course. The current case is presented with the radiographic feature of widening of the periodontal ligament space of the involved teeth, which is considered to be the earliest radiographic manifestation of osteosarcoma involving the jaw bone. The main aim of this case report was to focus on the importance of early diagnosis of this tumor based on clinical and radiographic examinations, and confirmation by histopathology. Considering the rarity of the disease type and particularly taking into account the fast progression and aggressiveness of this neoplasm, it is clear that the presentation of a clinical case represents a major contribution to better understanding of osteosarcomas involving the jaw bone.