Concentrated rice protein was prepared from the polished rice powder by the elimination of starch with bacterial amylase. Two groups of trained rats were fed 3g of this “high protein rice”. One and 3 hours after feeding, each group of rats were killed, the gastrointestinal contents were washed out and hydrolyzed with HCl. The remaining amino acids in gastrointestinal tracts were analyzed using an amino acid analyzer, and the amount of absorbed amino acids was calculated. Thirtyseven percent and 74% of injested nitrogen was absorbed 1 and 3 hours after feeding, respectively. Among the essential amino acids, Lys disappeared most rapidly from the gastrointestinal tracts, and Met disappeared most slowly. Thr and His belonged to the intermediate group. Similar experiment was carried out with a diet containing an amino acid mixture simulating rice protein. The absorption of nitrogen from this diet was 37 and 70 percent, 1 hour and 3 hours after feeding, respectively. The rate of absorption of each amino acid in this amino acid mixture was different from that of the previous experiment with rice protein. The rate of Lys, Met and Thr was intermediate, that of Arg and His was rapid. The absorption of Tyr was extremely slow. Relation to the supplemental effect of amino acids to rice protein was discussed.