Four mucous polyps obtained surgically from four male patients were studied electron microscopically, and following results were obtained. Epithelial cells of the polyps showed variation in thickness, cell composition and some fine morphological details. Superficial layer of the epithelium was composed of various combination of ciliated columnar cells, mucous cells, and non-ciliated epithelial cells. Basal cells formed basal portion of the epithelium. These epithelial cell components were held together by desmosomes however junctional complexes present between adjacent epithelial cells near the free surfaces showed no or poorly definable desmosomes. Intercellular spaces in the basal portion of the epithelium were generally wide, in which various migratory cells were observed. Epithelial layer was separated from subepithelial connective tissue by well defined basal lamina which, however, showed sometimes, gaps in which cell process from connective tissue was found. Stroma of the subepithelial connective tissue was generally edematous and contained flocculent materials and dense filamentous coagulated materials beside the collagenous fibers and various cellular elements but lacked the nervous tissue. Around the basal laminae of the surface lining epithelium and the blood vessels, dense filamentous materials were often accumulated and the cellular elementes were increased, indicating periphlebitis. Lack of nervous elements and vascular changes observed might be related to the nasal polyp formation and secondary changes might be followed in the epithelium.