A method for producing a purified soybean oligosaccharide liquid according to the present invention is a method for producing a purified soybean oligosaccharide liquid from a soybean and/or a processed soybean product, comprising: the step (1) of mixing the soybean and/or the processed soybean product with a water-containing polar organic solvent that contains a polar organic solvent and water and then removing a generated precipitate to obtain a soybean oligosaccharide liquid that contains the water-containing polar organic solvent; the step (2) of removing the polar organic solvent from the soybean oligosaccharide liquid to obtain a soybean oligosaccharide suspension; the step (3) of mixing the soybean oligosaccharide suspension with cellulase to obtain a cellulase-treated soybean oligosaccharide suspension; and the step (4) of subjecting the cellulase-treated soybean oligosaccharide suspension to solid-liquid separation to obtain a purified soybean oligosaccharide liquid.