This is a case of cemento-ossifying fibroma in mandible, one of fibro-osseous lesions arising in periodontal ligament, with review of literature for fibro-osseous lesions. En-bloc resection of mandible with alloplastic material (Pyrost(R)) was performed in cemento-ossifying fibroma of 20-year young male patient. By follow-up check of the patient, we obtained good result without any signs of recurrence.