In this study, bovine serum albumin (BSA) was covalently immobilized onto the surfaces of methyl methacrylate/methyl acrylic acid core-shell latex particles by the carbodiimide method, and the variation of the zeta potential of the BSA-latex complex as a function of the amount of BSA immobilized was measured. The experimental data revealed that the absolute zeta potential of BSA-latex complex exhibited a local minimum at 0.05 mg/m(2) of immobilized BSA. A two-layer model for the description of the electrophoretic behavior of the BSA-latex complex is proposed which is capable of explaining the behavior of the variation of the zeta potential as a function of the amount of BSA immobilized.