The snake commonly called Urutu cruzeiro is a viperid, which occurs in the Midwest and South of Brazil and Uruguay. This report aims to demonstrate an odontogenic neoplasm in a specimen of Bothrops alternatus. The same was referred to the Veterinary Hospital of Universidade de Passo Fundo RS - Brazil, weighing 0.4 kg, with a history of a bleeding pendulous lump in the oral region, firm and friable aspect. In clinical evaluation, there were pale mucous membranes and discomfort to close the mouth. In blood collection for pre-surgical evaluation, it was noticed anemia with a hematocrit of 12%. The patient was referred to anesthesia for nodular resection. After surgery the neoplastic mass was sent for histopathological analysis, in which was observed proliferation of cells similar to those that compose the dental pulp, having slightly rounded and flat contours and loosely arranged in star look with light background and with marked vascularity. The tissue sections were subjected to special colouring of Masson's trichrome, which can be observed by intense reddish impregnation, being these characteristics compatible with odontogenic myxoma. The day after surgery, the snake received morphine 1 mg/kg^-1 and enrofloxacin 2.5 mg/kg^-1 both SID, remaining the last for a week. After 90 days of nodular resection, the patient had no recurrence. The diagnosis of cancer in wild animals and especially reptiles requires intense experience. It is known that the literature about the subject is scarce, so the present case study was based on the available literature to domestic animals and humans.