Nasal polyps are commonly seen in the nasal cavity and paranasal sinuses. For past several decades, a great deal of study has been made, but nasal polyp still has much problems for the pathogenesis and its prevention. Recently the authors have made the study for electron microscopic findings and activity of Acid phosphatase in nasal polyp in order to clearify the more clear nature of the polyp, and the following results were obtained. 1) The histopathological findings in nasal polyp and normal nasal mucosa were obtained. 2) The epitheria of nasal polyp, which showed wide intercellular space with loose connection, contained the increased number of various wandering cells, polymorphor nuclear leucocytes, eosinophilic leucocytes and mast cells. In these number of eosinophilic leucocyte and mast cell would be strongly suggest that the relationship between allergy and nasal polyposis. 3) Many mixed secretory glands was observed in nasal polyp which has well developed Golgi appartus, rough endoplasmic reticulum and predominantly increased number of granules in cytoplasm. 4) Activity of Acid phosphatase in epithelium and secretory glandular cell of nasal polyp was relatively low and where it appeared to be scattered a small number of particle throughout the cytoplasm.