Kinetics of ion exchange separation of serine alkaline protease (SAP) by cation-and anion-exchangers, respectively, for the SAP + /H + and SAP -/OH -ion exchange reactions were studied with four different resins, i.e. low acidic Macro-prep CM, high acidic Macro-prep HighS, low basic Macro-prep DEAE, and high basic Macro-prep HighQ. The effects of pH on ion exchange equilibria were investigated within pH = 6.5-8.0 and pH = 9.5-11.0, respectively, for the SAP + /H + cation exchange and SAP -/OH -anion exchange reactions at T = 10-25 • C, and the results were interpreted on the basis of the theory of exchange of enzyme-ions. Although Macro-prep CM showed the highest SAP binding capacity at pH = 7.0, maximum recovery of SAP activity was obtained at 15 • C and pH = 6.5. Effects of feed concentration and flow rate were investigated in differential-(DIC) and integral (IC) ion exchange columns and 0.025 mol dm -3 and 1.0×10 -2 dm 3 min -1 gave the highest enzyme recovery as 70%. The overall internal-external mass transfer coefficient which was found by differential analysis showed the importance of liquid phase mass transfer resistances on the process under the operation conditions applied.