A functional chitosan derivative which comprises a chitin/chitosan, which is a natural polysaccharide, and incorporated therein at least one of a carbohydrate, a photo-reactive functional group, an amphipathic group, e.g. a polyoxyethylene alkyl ether, and a glycosaminoglycan and which, due to the incorporation, has solubility in a neutral medium, self-crosslinking ability, the property of highly containing water or healing wounds, and antithrombotic properties. Namely, the derivative has various properties required of health care materials such as medical products and cosmetics.