The aim of study was to obtain the main casein fractions (α_S1-CN, α_S2-CN, β-CN, and κ-CN) in preparative amounts using weak anion-exchangers. Total casein was obtained using isoelectric precipitation from fresh skim milk for fractionation. Fractional composition of total casein and the homogeneity of its fractions at different stages of the isolation were analyzed by electrophoresis on the vertical plates of polyacrylamide gel. At this stage, an alkaline buffer system containing 25 mM tris, 27 mM dietylbarbiturate, 3 mM ethylenediaminetetraacetate, and 4.5 M urea was used. Electrophoregrams were fixed and stained by conventional methods. The concentration of protein was determined by spectrophotometer (SF-46, λ-280 nm). Previously installed absorbtion coefficients for different fractions of casein (D 1% in 1 cm) were used: 10.0 – for α_S1-CN; 10,1 – for α_S2-CN; 4,6 – for β-CN; 9,6 – for κ-CN, and 8,2 – for total casein. DEAE-cellulose (DEAE-52 “Serva”) and toyopearl DEAE 650M (Toyo soda) were used as anion-exchangers. Batch separation of total casein was performed in 0.02 M acetate buffer (pH = 6.5) in the presence of 3.3 M urea and 0.01 M 2-mercaptoethanol. CaCl₂ was used as eluent. This salt is more effective than NaCl due to the interaction with phosphoserine groups of caseins. For fractionation we used the following concentrations of CaCl₂: 0.0 M (I fraction); 0.005 M (II); 0.01 M (III); 0.02 M (IV); 0.035 M (V); 0.05 M (VI).The experiment was replicated 3 times. As a result, electrophoretic analysis shows that κ-casein is found in fraction I; II contains β-casein; III and IV – α_S2-casein; V – α_S1-casein with minor impurities of α_S2-casein, and VI contains only α_S1-casein. Obtained fractions were dialyzed, lyophilized and weighed. The total yield of caseins was 71% using DEAE-cellulose and 77% in the case of anion-exchangers toyopearl DEAE 650M (P < 0.05). Weak anion-exchangers are more effective than strong ones in caseins preparative fractionation. It allowed us to obtain a separate group of α_S2-caseins, which includes α_S2-, α_S3-, α_S4-, and α_S6-caseins. These fractions are characterized by the same sequence of amino acid residues and are precursors of many original bioactive peptides.