Esophageal duplication constitute about 10% of all the mediastinal tumor and relatively rare condition. We have experienced one case of esophageal duplication which was found 2 years previously by radiologic study of chest, as mediastinal mass, in 37 years old male. He had neither clinical manifestations nor physical findings leading to the surgical discovery of the duplication. During the last 2 years, the size k location of the mass were stationary in character. Operative therapy of complete excision performed without surgical complication. On microscopic study, the lining cell of inner wall of cyst. Noted pseudostratified ciliated columnar epithelium with smooth muscle.