To provide a method for purifying an aminooligosaccharide, by which an aqueous solution of a salt is used without using hydrochloric acid in a method for producing an aminooligosaccharide or an aminooligosaccharide alcohol from a mixture of deacetylated aminooligosaccharides having various molecular weights or a mixture containing aminooligosaccharide alcohols prepared by reducing the mixture of the aminooligosaccharides.

The method for purifying an aminooligosaccharide comprises separating and purifying an aminooligosaccharide from a mixture of aminooligosaccharides with a cation exchange resin by using an aqueous solution of a salt as an eluate. The method is constituted of a purification process using a cation exchange resin once or a plurality of times or a process by another known purification method besides the purification process.