The present report describes a spontaneously developing, highly infiltrative, and expansile neoplasm in the mandible of a 9-month-old female Sprague Dawley rat. The lesion consisted of abundant odontogenic epithelium with induction of osteodentin in the adjacent mesenchyme and was classified therefore as an odontoameloblastoma. Odontoameloblastomas are reported uncommonly in domestic animals, and the histologic and histochemical features of this neoplasm are reported herein along with a review of the veterinary literature.