Evaluation of the submitted axillary mass confirms the diagnosis of chondroblastic osteosarcoma (OS) based on the cell morphology, the presence of osteoid deposit, and cartilage formation. Generally, metastasis (especially lung) is very common and arises early in the course of the disease, and some studies indicate that larger tumor size may be associated with a poor prognosis. The median survival time for dogs with appendicular skeletal osteosarcomas left untreated or treated with amputation alone is only 14–19 weeks. Improved survival times are now possible using adjuvant chemotherapy in conjunction with amputation or limb‐sparing surgery. Therefore further medical intervention, systemic emanation for metastasis, and close follow-up is recommended.*Previous study has established a histological grade system, which is thought to be predictive for the systemic behavior and metastatic potential of OS. By using the criteria of that study, the present case could be classified as Grade I to II OS. However, a more recent study found the histologic grading may not correlate with the clinical outcome.