The enzyme-catalyzed production of lactosucrose in a simulated moving-bed reactor is investigated. A numerical model is derived and verified by data obtained from simulated moving-bed reactor experiments. Based on the derived model, parameter studies and optimization are carried out. It is found that along with the flow rate settings, substrate feed and enzyme concentration and thermal deactivation of enzyme strongly influenced the product yield. Simulation showed that despite of parallel and consecutive side reaction, the maximum lactosucrose yield can reach 69%, which represents a yield increase of 36% relative to the equilibrium yield. (c) 2005 Elsevier Ltd. All rights reserved.