Odontoma is a common benign tumor in clinical practice, On the contrary, ameloblastic fibro-odontoma is a rare odontogenic tumor that consists of proliferation of odontogenic epithelium and mesenchymal tissue, the formation of dentine enamel tissue in tumor. We describe a case of odontoma developed in the molar part of the lower jaw in a 8-year-old girl, having difficulty in differentiating ameloblastic fibro-odontoma. She was referred to us with the chief complaint of delayed eruption of the right lower first molar. Panoramic X-ray films revealed a nearly oval unilocular image with irregular radiopaque lesion from the right molar to the ramus of the mandible. Clinical diagnosis was odontoma, and the lesion was enucleated under local anesthesia. Histopathological examination identified irregularly arranged enamel, dentin, and cementum, and intermingled soft tissue component mainly composed of proliferation of fibroblastic cells, partly intermingling with an island of enamel tissue. Although the pathological finding was similar to ameloblastic fibro-odontoma, final diagnosis was made as odontoma. Post operative course was satisfactory and the right lower first molar has gradually erupted.