Water-soluble dietary fiber provides numerous health benefits. A novel procedure to efficiently manufacture water-soluble indigestible polysaccharides was developed by heating glucose at 180°C in the presence of activated carbon. Aside from its ability to catalytically assist the polycondensation of saccharides, activated carbon provides the added benefits of being easily separable from the reactants and suppressing coloration of the product. Prior to purification, the indigestible fraction made up over 80% of the reaction mixture. After hydrolysis catalyzed by α-amylase and glucoamylase, and fractionation by ion-exchange chromatography, a total of 99.7% dietary fiber content was attained. This indigestible fraction, termed resistant glucan, was only minimally degraded by upper digestive tract enzymes, similar to the digestibility of polydextrose. Structural analysis by methylation and NMR indicated that the resistant glucan formed a highly branched structure containing α- and β-1,2-, 1,3-, 1,4-, and 1,6-linkages. On an industrial scale, the resistant glucan was obtained from glucose syrup (DE 86) by heating with activated carbon, enzymatic hydrolysis, refining, fractionating, and drying. Our facile method is an efficient means to obtain water-soluble dietary fiber.