The process for GOS production from whey lactose involves two sequential immobilized enzyme reactors and a chromatographic separation process for purification of GOS. Lactases, ß-glycosidase enzymes, from Aspergillus oryzae(mold) and Bacillus circulans (bacterium) were used to convert lactose to GOS by a transgalactosylation reaction. Products containing 28% of GOS (at 50% conversion) and 40% of GOS (at 60% lactose conversion) were obtained using lactase from A. oryzae and B. circulans, respectively. Two sequential plug-flow reactors with the immobilized ß-galactosidases were used to convert lactose (400g/L) to GOS with a high productivity of 200 g/L/h, which is about 100-fold higher than most other processes. To further increase the GOS content in the final product, a simulated moving bed (SMB) chromatographic technique was studied to separate GOS from lactose and monosaccharides. SMB offers a high efficiency due to the continuous operation and efficient use of the mobile and stationary phases, allowing high sample loading with improved productivity and saving 90% in solvent consumption as compared with conventional liquid chromatography methods. The chromatographic separation process was optimized in several parameters: a) the amount of cross linking in the stationary phase, b) the choice of counter ion, c) the effect of temperature, e) the particle size of the resin beads, and e) the effect of flow rate.