Epidermal cyst in the floor of mouth is relatively rare disease. Patients usually present soft and non-tender mass at the midline of mouth floor. Careful history taking and imaging study are needed for the diagnosis and surgical excision is the choice of treatment. We report a case of huge epidermal cyst located in the floor of mouth mimicking plunging ranula, which was successfully removed by transoral surgical excision without any complication. It was diagnosed as an epidermal cyst by pathologic examination.