Concentration of acid centers in a commercial ion exchanger catalyst was controlled by partial neutralization of sulfortic groups with various primary. secondary and tertiary amines of different molecular size. The effect of the acid center concentration on catalytic activity of the ion exchangers was tested by measurements of initial reaction rate of re-esterification of ethyl acetate with I-propanol in a CSTR-type reactor. There was found much higher than proportional dependence of the catalytic activity on the degree of the neutralization and the efficiency of various amines in the activity suppression decreased roughly in the order tertiary > secondary > primary. (c) 2004 Elsevier B.V. All rights reserved.