Chitosan, a natural polymer obtained by alkaline deacetylation of chitin, is non-toxic, biocompatible, and biodegradable. Various chitosan molecular weights (MW) have been designed, from high MW to low MW chitosan oligosaccharides (COS). Chitosan has excellent antibacterial, moisture retention, biocompatibility, safety, and chelating properties, and numerous chitosan products are currently being developed to take advantage of these properties. These properties have made chitosan an excellent carrier for drug delivery and a functional food. This chapter presents examples of oral administration for chitosan, COS, and their derivatives, especially in the medical and pharmaceutical fields and as oral drug delivery carriers.