Osteosarcomas are primary malignant bone tumors in which mesenchymal cells produce osteoid. It is generally the most common malignant bone neoplasm, although lesions of the jaw are uncommon. Osteosarcoma of the Jaw (JOS) presents a lower incidence of metastasis and a better prognosis than osteosarcoma of the long bones. However, patients with JOS can exhibit advanced tumors, mainly when early diagnosis is not performed. This article reports on a case of an advanced osteosarcoma of the mandible. A 16-year-old lady came for evaluation and treatment of lower jaw mass. The patient had been noticing loose teeth and progressively enlarging mass since 3 months. Computed tomography showed large heterogenous lesion measuring 8.4 × 6.8 cm arising from mandible with cortical destruction and periosteal reaction. She had undergone incisional biopsy which revealed ill circumscribed subepithelium tumor with alternating areas of chondromyxoid and fibrocellular components, foci of osteoid formation, areas of ischemia type of necrosis, abscess formation and established the diagnosis as osteosarcoma of bone chondroblastic type. The patient was then recommended for oncologic treatment with 2 cycles of pre-operative chemotherapy. She received 1 cycle NACT (adriamycin+cisplastin), but as the disease was progressing quickly, so she was referred to our centre and underwent surgery.