The nutrients content and amino acid composition of 4 naked and 2 covered oat cultivars were determined. The effect of 0,25% L-lysine or 0,1% β-glucanase supplemantation on the biological value (BV) and true digestibility (TD) of the oats protein were evaluated on rats using the Thomas-Mitchell method. The L-lysine supplement resulted in the higher BV (P < 0,01) only in the case of naked STH 296/91 cultivar, which contained the lowest amount of lysine. The addition of enzyme preparation improved TD of oats protein, but these differences were statistically significant only in the case of naked cultivar STH 2795 (P < 0,01).