Adenocarcinoma not otherwise specified (NOS) is a malignant salivary gland tumor without the histological characteristics of other salivary gland tumors. It rarely occurs in the small salivary glands and development in the molar glands is extremely rare. We report a case of adenocarcinoma NOS occurring in the retromolar pad. The patient was a 75-year-old woman with a protrusive 10 × 15 mm mass in the retromolar region. The lesion was elastic soft and had an irregular surface. Biopsy resulted in a histopathological diagnosis of adenocarcinoma NOS. No regional or distant metastasis was observed in imaging. The tumor was successfully resected under general anesthesia. The postoperative course was uneventful and there has been no recurrence or metastasis seven years after the surgery.