To provide a simple method for producing an acidic xylooligosaccharide, by which the acidic xylooligosaccharide having 2-5 average polymerization degree of xylose can be produced in large amount, as well as, at low cost.

The acidic xylooligosaccharide, having uronic acid residue, is obtained by subjecting wheat bran and/or rice bran to heat treatment, with hot water at 100-150C to obtain a sugar solution, and subjecting the resulting sugar solution to ion exchange treatment. The heat treatment with hot water is, preferably, carried out under acidic condition of a pH range of 1.0-4.0, or under alkaline condition of pH range of 9.0-13.0.