Middle ear mucosa of the normal rats were studied using the light microscope. The promontory was lined by flat cells with scanty subepithelial layer. The anterior bulla was lined mostly by non-ciliated cuboidal cells or flat cells with few ciliated cuboidal cells. The lower most part of the anterior bulla was covered by ciliated columnar cells or goblet cells with some non-ciliated columnar cells. The Eustachian tubal area was lined by ciliated columnar, ciliated euboidal or goblet cells. The result of this study suggests the precence of active mucociliary transportation system in the tympanic bulla of the rats.