Galactosyl-oligosaccharides (GOS) are non-digestible oligosaccharides which are qualified as functional foods. GOS are enzymatically synthesized from lactose by transgalactosylation catalyzed by the enzyme P-galactosidase. In this study, a method for immobilization of O-galactosidase from Kluyveromyces lactis on a chromatography membrane was developed. The immobilization was performed at 4, 15 and 40 degrees C. A strong basic anion exchange membrane was investigated. In static experiments the highest enzyme activity was measured at an immobilization procedure temperature of 15 degrees C. The immobilization on the chromatography membranes was found to be very rapid likely due to ionic adsorption. The synthesis of GOS was carried out in a Continuous Membrane Chromatography Reactor System (CMCRS) at 40 degrees C and pH 7.0 using 20 wt% initial lactose concentration. The chromatography membranes proved to be a good support for the continuous process at high convective flow rates in the enzyme reactor system. Up to 82 % lactose conversion with 24 % GOS yield was achieved at different fluxes. The corresponding reactor productivity for the production of GOS from lactose in the CMCRS was 98.7 g GOS per hour and cubic centimeter membrane volume, which significantly exceeds previously reported results.