Keratan sulfate localize in tissue as of keratan sulfate proteoglycan, known as one of the glycosaminoglycans. Keratan sulfate is composed of repeating disaccharide of galactose and N-acetylglucosamine, and shows diversity by the number of the sulfation on the sugar chain.

Keratan sulfate is a well known for existing in cornea and in some cartilage, and a new type of keratan sulfate proteoglycan has also recently been found in brain tissue. The detection of keratan sulfate from various types of biological sample is attracting attention for purpose of the functional analysis of keratin sulfate and for working out its relevancy with various diseases.