Cystadenoma is a benign epithelial tumor and usually occurs in the ovary. In the oral and maxillofacial region, the tumor occurs in the salivary gland, but the frequency is very low. We report a case of cystadenoma arising in the lower lip of a 50-year-old woman. She noticed a swelling in the lower lip 8 years previously. The mass was elastic soft and painless. The tumor was covered with normal mucosa, and the size was about 10 mm in diameter. Magnetic resonance imaging of the lesion showed low intensity on T1-weighted images and high intensity on T2-weighted images. The clinical diagnosis was a benign salivary gland tumor, and we surgically excised the tumor with the patient under local anesthesia. Histopathologically, the tumor had cystic spaces lined with squamous and cuboidal epithelial cells. There was no cellular atypia or mitotic figures. The histopathological diagnosis was cystadenoma. There was no evidence of recurrence 1 year 5 months after excision.