To obtain a novel cationic unsaturated saccharide of high purity giving a polymer which is stable under both acidic and alkaline conditions and is useful for cosmetics, ion-exchangers or auxiliary agents for paper in high yield by reaction of a deoxyaminosaccharide with an allyl compound.

This novel cationic unsaturated saccharide is represented by formula I (R1 is a deoxysaccharide bearing 1-20 monomer units; R2 is R1, a 1-20C alkyl, a 2-20C alkenyl, polyoxyethlylene, polyoxypropylene, polyethyleneimine; R35-R5 are each H, methyl; X is a halogen, tosilate ion, an aryl sulfate ion) and the cationic polymer therefrom is useful as a cosmetic, ion exchanger, an auxiliary agent for paper or waste-water-treating agent. This compound is obtained by reaction of a deoxyaminosaccharide represented by the formula: R1R2NH with an allyl compound represented by formula II.