The author have recently experienced a case of huge epideral retention cyst which was known as a rare disease and developed in the floor of the mouth. A 25 year old female visited the department of otolaryngology because of swallowing difficulty and considerable discomfort due to a large soft mass and swelling in the submental region and the mouth floor. A cyst was completely removed transorally under the local anesthesia. It was globular shape, 8×4.5×2cm in size, 40gm in weight, and its content was yellowish cheese like material, and was confirmed in pathology.