The amylase system of black-koji molds was fractionated, in respect to its activity, into two fractions, the dextrinogenic and saccharogenic. Their separate and combined activities to digest raw starch were investigated. Contrary to the knowledge established so far, the dextrinogenic amylase fraction was found to be capable of digesting the raw starch though only weakly, while the saccharogenic amylase fraction much more strongly. When the two fractions were combined, digestion proceeded with twice or thrice the velocity of the, sum of each component. This accelerating interaction, which never occurs in cooked-starch digestion, is worthy to be stressed as a characteristic of raw starch digestion by this amylase system. The raw starches of corn, wheat and glutinous rice are in this way, digested completely to glucose. Among them, glutinous rice starch displays peculiar facility in the digestion.