We report a case of odontogenic fibroma in the mandible.The patient, a three year-old boy, was referred to us for swelling in the right mandible. Oral examination revealed bony expansion of the right lower deciduous molar region. Panoramic radiography showed a well demarcated radiolucent lesion including E and extending from the D to 6 region.A 5 tooth germ was not found. The lesion was enucleated under a tentative diagnosis of odontogenic tumor. The material was 30 × 20 × 20 mm in size and elatsitc soft in consistency, and the cut surface was solid. The roots of E adhered to the tumor. Histologically, the tumor was fibrous tissues consisting of cells with fusiform and ovoid nuclei resembling dental papillae. There was no evidence of cellular atypia or calcifying materials in the tumor. Odontogenic epithelial cells of various types, ranging from tall columnar with polarization of the nuclei to flattened structures, surrounded the tumor tissue but did not exist in the tumor.