There had been many research about histopathologic study in chronic paranasal sinusitis by means of light microscope. There have been many trials in the study of ultrastructure in many aspects by means of electron microscope in recent years. Now, in order to observe ultrastructural change of epithelium in mucous membrane of maxillary sinus that occurs in chronic paranasal sinusitis, the author took the electron microscopic pictures of the mucosa, removed from maillary sinus during paranasal sinus surgery in our hospital and was led to following conclusions such as. 1) There were structural changes in the cilia in the ciliated columnar epithelium, such as change in number of microtubule, appearance of compound cilia and conglomeration of microvilli ets. 2) In goblet cell, swelling of Golgi complex and appearance of multivesicular body in mucous granules were found. 3) We didn't find any difference in the ultrastructure of mucosa between atrophic type and hypertrophic type.