The composition and nutritive value of protein of three new lines of Polish naked oat were compared with husked oat, wheat and maize. In all cereals, lysine was the first limiting amino acid but its content was higher in both types of oat than in wheat and maize. The chemical score of naked and husked oat was thus higher than of other cereals; the EAA index of naked oat was the highest. True digestibility (TD) of naked oat protein was significantly higher than of husked oat and did not differ from TD of wheat and maize. Biological value (BV), and NPU of naked oat protein were significantly higher than of other cereals. PER coefficients determined in a growth experiment were higher in both types of oats than in maize and wheat. Supplementation with lysine increased PER values of all cereals but a significant effect was found only in maize.