It is difficult to detect and diagnose a mass at the tongue base, particularly if the mass is located under normal appearing mucosa. Computed tomography (CT), particularly post-contrast images, is useful to evaluate a tongue mass and adjacent structures including cervical lymph nodes. Nevertheless, a definitive diagnosis of a mass is obtained by histopathological examination. In this case, we describe a mass arising from the tongue body to the root in a dog. The patient was referred with ptyalism and an eating disorder. An oral examination was performed, and decreased tongue motility was observed. CT scanning was performed, and a lingual mass was detected. A lingual mass sample was collected by biopsy at the postmortem 2 months later. A histopathological examination was performed, and the lingual mass was diagnosed as squamous cell carcinoma.