Ameloblastic fibrosarcoma (AFS) is a rare malignant odontogenic neoplasm. It is composed of a benign epithelial component and a malignant ectomesenchymal component and most frequently seen in the third and fourth decades of life. Mandible (posterior part) and maxilla is most commonly involved. We report here a case of AFS originating in the mandible of long term duration of eight years. The presentation suggests malignant transformation of benign ameloblastic fibroma in the present case. The patient was treated by surgical excision followed by radiotherapy.