Disclosed is a cellulose derivative which is obtained by substituting a part of a plurality of carboxyl groups in a carboxymethyl cellulose, which is a cellulose derivative, with -CO-NH-X-CO-Y-Z. Also disclosed is a hydrogel of the thus-obtained cellulose derivative. In this connection, X represents a divalent hydrocarbon group having 1-10 carbon atoms Y represents a divalent group derived from a polyalkylene oxide, which has an oxygen atom at both ends Z represents a hydrocarbon group having 1-24 carbon atoms or -CO-R
