Regularities of bovine serum albumin sorption on carboxylic cation-exchanger have been studied. The porous cation-exchanger was synthesized by terpolymerization of methacrylic and acrylic acids and cross-agent. The influence of sodium chloride concentration in interval 0-0.3 M and the solution pH value (4.5, 5.0, and 5.5) on albumin sorption has been considered. Sodium chloride concentration influence on protein sorption was shown to have different character depending of solution pH value. Salt concentration increase in studied interval causes protein sorption increase at pH 4.5. The cation-exchanger capacity dependence from salt concentration at pH 5.0 is characterized by curve with slight maximum. The increase of sodium chloride concentration from 0.1 till 0.3 M in solution having pH 5.5 leads to sharp decrease of protein sorption. The interpretation of regularities found was done considering functional groups` ionization degree change. Sodium chloride concentration and solution pH influence on the sorbent specific swelling has been shown. Specific swelling of cation-exchanger changes differently with salt concentration increase at different solution pH values.