The potential chemopreventive properties of the dietary fiber prepared from sweetpotato (Ipomoea batatas L.) roots were examined to promote the demand of this residue from the starch industry. Dietary fiber was prepared by treating starch granules-removed residue with α-amylase. The dietary fibers at 1% concentration enhanced the growth of Bifidobacterium adolescentis and Bifidobacterium breve in vitro among 5 species of Bifidobacterium, which exist in the human intestinal tract. Analysis of the components of these fibers suggested that their pectin and hemicellulose were concerned with a promotion effect on the growth of bifidobacteria. Water- and oil-holding capacity of the fibers in the varieties with orange-colored flesh was relatively superior to ones from the varieties with yellow- or purple-colored flesh. Furthermore, the dietary fibers adsorbed about 90% of the mutagen, Trp-P-1. Commercial sweetpotato fiber, a byproduct of citric acid production from the residue from the starch industry, had slight effect on the growth of bifidobacteria and was lower in adsorption capacity of Trp-P-1 than the fibers prepared from sweetpotato roots. These results indicate that the residue from the sweetpotato root starch industry is available as a dietary fiber with physiological functions.