Enzymatic membrane reactors were obtained from polymeric membranes and activated carbon, and used for oligosaccharide purification. The activated carbon was used to adsorb the enzyme, directly or via a metal ion as intermediate. We studied the adsorption capacity of two activated carbons (a commercial carbon and a home-made one) and the formation of the complex. In a second step, we studied the activity of the enzymes in batch experiments, and analyzed the synthesis and performance of the membrane reactors. Different kinds of enzymatic membrane reactors were obtained with immobilized solid enzymes. Our results show good agreement between the kinetics of the reactions and the velocity of the flux across the membrane, since both reaction and separation were properly achieved. We also determined optimum amounts of enzyme for obtaining the desired products with a low degree of polymerization and low concentrations of monomer. (c) 2005 Elsevier B.V. All rights reserved.