 Previous reports indicate that inacetyldeglucosamine oligomers, chydenoligosaccharide, knock-os, and deglucosamine oligomers, chytosanoligosaccharide, COS, have various biological activities, especially against cancer and inflammation. In this review, we have summarized the findings of previous investigations that have focused on anti-cancer or anti-inflammatory properties of knock-os and COS. Moreover, we have introduced recent evaluation of knock-os and COS as functional foods against cancer and inflammatory disease. This article was authored by Kazuo Azuma, Tomohiro Osaki, Saburo Minami, and others.