Abstract: Osteoblastomas are rare tumors accounting for approximately 1% of all primary bone tumors. We report a case of osteoblastoma of the mandible with high FDG uptake. Initially, this lesion was judged as an osteosarcoma. Osteoblastomas are benign slow-growing tumors. High-resolution thin-slice CT images of the lesion as part of the PET/CT study help to characterize its morphology and extension, thus facilitating biopsy planning and resection. Approximately 25% of osteoblastomas initially have the imaging appearance of a malignant tumor. In our case, complete resection of the lesion followed by reconstruction with a bone graft was performed.