Dynamic surface elasticity of the solutions of β-casein-surfactant complexes are measured by the oscillation barrier method as functions of surface age and surfactant concentration. Small amounts of added ionic surfactants greatly affect the kinetic dependence of dynamic surface elasticity. The pattern of kinetic dependence is determined by the sign of the charge of surface-active ion. Results obtained can be explained if we take into account the strong electrostatic interaction between charged amine acid residues in the protein and surface-active ions, as well as different distribution of positive and negative charges along the protein chain. The proposed recently mechanism of adsorption of β-casein, which suggests the consecutive formation of loops and tails from relatively hydrophilic and hydrophobic parts of protein molecule, is confirmed. © 2009 Pleiades Publishing, Ltd.