Dysfunction of mucociliary clearance system develops the pooling of nasal secretion in the nasal cavity and is a common cause of vicious cycle of symptoms in chronic paranasal sinusitis. So, we investigated the morphological changes of nasal mucosa in chronic paranasal sinusitis using light and transmission electron microscopy(TEM). The nasal mucosa was taken at bulla ethmoidalis during endoscopic sinus surgery sized in 5×5mm. The light and electron-microscopic examination of specimens showed increased number of goblet cells, non-ciliated cells, submucosal glands and inflammatory cells, decreased number of ciliated cells, deformation of cilia, and metaplasia in nasal epithelial lining and so on. Therefore, decreased numbers of ciliated cells and increased thickness of mucous layer might cause the mucociliary dysfunction in chronic paranasal sinusitis.