A diverticulum is a pouch of the digestive tract mucosa that penetrates the muscular layer because of a partial defect in the muscle. It has often been reported in the digestive tract mucosa, but is extremely rare in the oral cavity. We report a case of a diverticulum-like lesion of the buccal mucosa. A 60-year-old man visited his regular dentist for dental treatment. An atheroma-like lesion was noted near the papilla of the parotid duct in the right buccal mucosa. The right maxillary molar was extracted because of a suspected odontogenic infection, but his symptoms did not improve, and he therefore consulted our hospital. Two pouches, one measuring 10 mm in depth and the other 5 mm in depth, were noted, and both contained food debris. These lesions were diagnosed as diverticulum-like lesions of the buccal mucosa and were resected with the patient under general anesthesia. A partial defect of the buccinator muscle was recognized under the pouch. Histopathologically, the buccal mucosa penetrated the buccinator muscle and reached the fatty layer, and buccal glands were located at the bottom of the pouches. These findings suggested the etiology of this lesion. No recurrence has occurred as of 1 year 6 months after surgery.