Konjac glucomannan (KGM) was enzymatically hydrolyzed and mechanically sheared. KGM molecular weights were reduced by both enzymatic hydrolysis and shearing. Most lactobacilli fermented KGM hydrolysates, while most bifidobacteria did not. Human gastrointestinal bacteria can utilize KGM hydrolysates with reduced weights. KGM hydrolysates with reduced weights have potential for use as prebiotics.