Abstract: The adsorption equilibrium of bovine serum albumin (BSA) on a porous anion exchanger DEAE-Spherodex M in acetate buffer was studied by batch adsorption experiments. The steric mass action model (SMA) was used to express the adsorption isotherms. By linear chromatography experiments and the nonlinear least square fitting method, the SMA model parameters were determined. It was found that the characteristic charge and the steric factor became constant at pH values much higher than the isoelectric point of BSA, and ionic strength had a significant effect on the equilibrium constant by affecting the intensity of electrostatic interactions between BSA and the surface of the anion exchanger.