The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. In humans, it measures about 1 inch wide by 2 inches long (about 2 cm by 5 cm) and lies on the roof of the nasal cavity about 3 inches (about 7 cm) above and behind the nostrils. The olfactory eipthelium is the part of the olfactory system directly responsible for detecting odors.

The tissue is made of three types of cells: the olfactory receptor neurons which transduce the odor to electrical signals, the supporting cells which protect the neurons and secrete mucus, and the basal cells which are a type of stem cell that differentiate into olfactory receptor neurons to replace dead receptor neurons. The olfactory epithelium is divided into four zones from ventral to dorsal. Each olfactory receptor is expressed throughout one zone.

The olfactory epithelium can be damaged by inhalation of toxic fumes, physical injury to the interior of the nose, and possibly by the use of some nasal sprays. Because of its regenerative capacity, damage to the olfactory epithelium can be temporary but in extreme cases, injury can be permanent, leading to anosmia.