The biological value of sunflower meal, alfalfa meal, brewer's dried grains and some other feedstuffs proteins is impaired drastically due to the enormous amounts of lignocellulosic matters in these feedstuffs. Thus, the problem when using these feedstuffs in poultry and swine feeding is just this impairment of the proteins. The intend of this work is to examine the possibilities for mechanical fractionation of sunflower meal, alfalfa meal and brewer's dried grains into the protein and cellulose fraction and to study the influence of different screen hole sizes on the yield and quality of the final products. The fractionation of the sunflower meal and brewer's dried grains was carried out in a separator with the 1.5, 2.0 mm screens and of the alfalfa meal with the 0.6, 0.8, 1.0, 1.2, and 1.5 mm screens. Based on the experimental data on the technical efficiency of fractionation it can be concluded that the crude protein content was significantly increased with a concomitant reduction in the crude fibre content in fine fraction (passing material) of all feedstuffs investigated. The gradual decreasing of screen hole diameter rendered the logical and regular increase of crude protein content by 3.6% in sunflower meals, 3.75-6.83% in alfalfa meal and 5.2-9.0% in brewer's dried grains. Concomitantly, the content of crude fibre in the fine fraction that passed through the screen (passing material) was reduced by 3.3-6.7%, 4.22-7.23% and 1.7-4.7% in sunflower meal, alfalfa meal and brewer's dried grains, respectively.