We experienced the rare case of a malignant oncocytoma which arose from a minor salivary gland of the buccal mucosa. The case was a 57 year-old male with a small mass in his buccal mucosa as the chief complaint. External irradiation to the local field was performed after surgical removal of the primary lesion. Due to the presence of cervical metastasis, however, a left neck dissection performed 5 months later. The tumor cells were large, and acidophilic granules filled their cytoplasm. The nuclei were large and had very clear nucleoli. A tendency towards invasion into the veins and lymph ducts was also seen observed. These findings satisfied the clinical and pathohistological criteria for a malignant oncocytoma.