Most of the macroglossia, which is very rare disease, comes from congenital origin. Congenital macroglossia generally results from lymphangioma or hemangioma but in some cases happens idiopathically. Recently the authors experienced a case of congenital idiopathic muscular macroglossia. Patient is 6 year old girl whose tongue was enlarged and protruded from mouth since birth. The size of protruded tongue from upper lip was about 7.5×6.0×3.0cm and its surface was dry and fissured. The histopathological section shows hyperkeratosis of surface epithelium with elongation of rete ridge and hypertrophy of muscle layer. Therefore it was diagnosed as congenital muscular macroglossia.