Abstract: The ion-exchange equilibrium of bovine serum albumin (BSA) on an anion exchanger was studied.The usefulness of steric mass-action (SMA) model was analyzed for describing protein ion-exchange equilibrium in different buffer systems.The results showed that the SMA model was useful in the prediction of protein adsorption decrease with increasing ionic strength in a wide pH range.However,at higher salt concentrations where very low protein adsorption was achieved,the model predicted adsorption capacity was higher than the experimental results.At lower pH close to the isoelectric point of BSA,the accuracy of the model prediction further decreased.It is considered that the SMA model could be further improved by taking into account the factors influencing the three-dimensional structure of proteins (e.g., pH) and the effect of salt concentration on the intermolecular interactions of proteins.