Osteosarcoma (OSA) is the most common primary bone cancer diagnosed in dogs and characterized by proliferation of osteoblastic malignant mesenchymal cells that produce osteoid bone or immature, non-reactive character or being metaplastic. We report a case of a female Poodle 12 years of age and 12 kg, with an increased volume in humeral-radioulnar of the right forelimb. After clinical and complementaryit was observed uneven bone architecture of the proximal radius, whose cytological and histological examinations confirmed that it was chondroblastic OSA. The treatment was performed to limb amputation and chemotherapy indicated the animal, which was not realized at the option of the owner, who by the age of the dog and the emergence of side effects, preferred to keep her pain medication as necessary. It was clarified that the death of the animal would most likely be by action of pulmonary metastases. This case is interesting because it is a small dog, being affected by OSA in canine uncommon anatomical location.