 Previous reports indicate that n-acetyldeglucosamine oligomers, chydenoligosaccharide, NACOs, 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 NACOs and COS. Moreover, we have introduced recent evaluation of NACOs and COS as functional foods against cancer and inflammatory disease.