This is a case report of a florid osseous dysplasia occurred in the left posterior region of the mandible in a 60-year-old female. Florid osseous sysplasia is a distinct clincial pathologic entity representing an exuberant variant of osseous dysplasia, defined by Robinson to be a abnormal reaction of bone to irritation or stimulation. The treatment was performed with partial mandibulectomy and immediate reconstruction with metal plate and iliac bone graft. The patient did well postoperatively and has shown no sign of recurrence or complication during the 6 month postoperative period.