This work reports a systematic study on the effects of ionic environment on the adsorption of alpha-amylase on 30 kDa polyether sulphone (PES) membranes on the basis of interfacial interaction of PES membrane and alpha-amylase enzyme in solution. Static adsorption of alpha-amylase was investigated at the solution pH values of pH = 4.5, 5.6 and 7.0; and for the ionic strengths of 0.001, 0.01 and 0.1 M KCl. The maximum adsorption occurred at the pH value below the isoelectric point (IEP) of the enzyme, whereas the minimum adsorption occurred at the IEP (pH = 5.6) of amylase. With increasing ionic strength, the adsorbed enzyme on the membrane decreased. The Freundlich and Langmuir adsorption models were used for the mathematical description of the adsorption equilibrium and isotherm constants were evaluated depending on ionic environment. To determine the steps affecting the adsorption mechanism, the experimental data were evaluated using pseudo-first-order and pseudo-second-order kinetic models. The experimental data fitted well the pseudo-first-order kinetics. To detect the structural changes which occurred, membrane surfaces were analyzed by FTIR-ATR spectroscopy. The effects of ionic environment on amylase activity were also investigated. Copyright (C) 2010 John Wiley & Sons, Ltd.