Anatomy of oral cavity in Down syndrome is characterized by hypotonic macroglossia, small oral cavity, narrow palate with high-arch shape and hypertrophy of tonsil and adenoid. Because of such a anatomic characteristics, they show difficulty in respiration, mastication, swallowing and articulation. So far we operated on 135 children with Down syndrome for partial glossectomy in average volume of 4.6cc. This study is histopathologic finding of partially resected tongue in 4 cases, analyzed by histochemical stain and electron microscopy. The results of histochemical study showed predominant of Type 2 myofiber and interstitial edema, fibrosis and chronic nonspecific inflammation. In the study of electron microscope, the size and number of mitochondria were increased, but structural abnormality was not showed.