In the Republic of Kazakhstan, pressing of flax seeds (squeezing) is most often used, therefore cake is more common than meal and its resulting physical reserves exceed meal several times. The biochemical characteristics of the protein complex of flaxseed have not been sufficiently studied, which, in our opinion, limits the use of protein products obtained from flax seeds such as flaxseed cake in the production of compound feed for farm animals and poultry. The article presents studies of the protein complex and amino acid composition of flaxseed cake of the Kazakhstan variety “Kostanay 11”. Flaxseed cake contains 36,5% protein, the fat content is 7,5%. The fractional composition of flaxseed cake was compared with the flax varieties “Northern” and “Golden” grown in the Republic of Kazakhstan. The amino acid composition of flaxseed cake was compared with other cakes used in feeding farm animals and poultry. The purpose of the study is to study the fractional composition of the protein complex of flaxseed cake from flax variety "Kostanay 11". A characteristic feature of the protein complex of flax seeds is the high total content of water- and salt-soluble proteins – albumins 29,2% and globulins 16,8%, which are considered well digestible. Flaxseed cake from flax variety "Kostanay 11" in its amino acid value is equal to the known cakes common in feed production and is second only to soybean cake. This allows us to assert that flaxseed cake obtained from the seeds of the “Kostanay 11” variety remained a highly digestible and highly nutritious product in terms of protein absorption, suitable for its inclusion in the diets of all types of farm animals and poultry, starting with feed for young animals.