Keratin 18 is a type I cytokeratin. It is, together with its filament partner keratin 8, perhaps the most commonly found products of the intermediate filament gene family. They are expressed in single layer epithelial tissues of the body. Mutations in this gene have been linked to cryptogenic cirrhosis. Two transcript variants encoding the same protein have been found for this gene.

Human keratin 18 and the homologous mouse Endo B are type I IF protein subunits whose expression is restricted in adults to a variety of simple epithelial tissues. Endo B and its coexpressed type II keratin, Endo A (the mouse equivalent of human keratin 8), appear to be the first IF proteins expressed during murine development.