To provide a stable composition for bleaching, highly safe to a human body, and having excellent effects; and to provide an external preparation for the skin, containing the composition.

The composition for the bleaching contains an acidic xylo-oligosaccharide composition of a mixed composition of oligosaccharides having an uronic acid residue in one molecule of the xylo-oligosaccharide and different polymerization degrees of xylose, and having 5.0-15.0 average polymerization degree of the xylose. The acidic xylo-oligosaccharide composition is obtained by enzymically treating a lignocellulose material to provide a complex of the xylo-oligosaccharide component and a lignin component, hydrolyzing the complex with an acid to provide a xylo-oligosaccharide mixture, and separating the acidic xylo-oligosaccharide composition from the xylo-oligosaccharide mixture. Preferably, the uronic acid is glucuronic acid or 4-O-methyl-glucuronic acid. The composition for the bleaching contains 0.001-30 mass% acidic xylo-oligosaccharide.