To provide an external preparation which has an improving effect on atopic dermatitis and has high safety.

This external atopic dermatitis-improving preparation contains an acidic xylooligosaccharide having uronic acid residues in the molecule as an active ingredient. The acidic xylooligosaccharide is preferably a mixture composition of the oligosaccharides having different xylose polymerization degrees and having an average polymerization degree of 5.0 to 15.0. The uronic acid is especially glucuronic acid or 4-O-methyl-glucuronic acid. The acidic oligosaccharide is economically obtained by enzymatically or physicochemically treating a lignocellulose material to obtain the complex of the xylooligosaccharide component with the lignin component and then subjecting the complex to an acidic hydrolysis treatment.