The relative nutritive value (RNV) of protein in the several kinds of food were tested with young rats by the slope-ratio assay using gain as response and nitrogen intake as the measure of dose which was proposed by Hegsted (1965). Ten different foods were tested.The relative nutritive value of wheat gluten were 29 and 31; casein 68 and 70; hen's egg 113; egg pattern amino acid mixture 109; cow's milk (skim milk powder) 95; white rice 70 and 71; white rice+0.2% Lys+0.1% Thr 104; rice bran protein 90 and barley 53. In addition the RNV of a Japanese diet containing about 40% of animal protein was 83, and was similar to the biological value (85) or net protein utilization (78), previously determined.