Osteosarcoma is an aggressive malignant osea neoplasm of rapid proliferation, of mesenchymal origin, formed by osteoblasts characterized by the production of osteoid material or bone matrix, with a high probability of metastasis even after the surgical reception of the tumor, usually presents itself in large breed animals - giants with an average of 7 years, affecting the appendicular apparatus in greater proportion than the axial apparatus, one of the most malignant tumors in veterinary medicine and among the 4 most common tumors of the oral cavity. During this work was done the clinical following case of a canine with osteoblastic osteosarcoma in the oral cavity during a period of 16 months, which was subjected to the surgical technique of bilateral subtotal mandibuletomy that is proposed as a less traumatic alternative to the choice technique, the total mandibulectomy, was performed at the veterinary clinic of the Catholic Pontifical University of Paraná, Curitiba-Brazil