Introduction: Osteosarcoma (OS) is primary malignant bone tumor in which mesenchymal cell produce osteoid. OS of jawbones is uncommon, representing 4-8% of all OS.

Case Report: This paper reports the case of a- 29 year-old female with an OS in mandibular first molar as exophitic lesion with smooth surface during 1 year. Based on the patient's symptoms, differential diagnosis was lymphoma and malignant meshenshymal tumors. Exci-sional biopsy was done and histopatholigic feature proved to be OS.

 Conclusion: Postoperatively, the patient was referred to the oncology department of Tehran Imam Khomeini hospital for further evaluation and treatment.