Experimental studies were made for immobilization of enzymes on microporous polyvinylidene fluoride (PVDF) membrane in order to carry out enzymatic reaction of lactose into galacto-oligosaccharides using beta-galactosidase. The present work, however, is the first part in the direction of enzymatic membrane reactor studies for carrying out reaction followed by membrane based separation to purify galacto-oligosaccharides out of reaction mixture. The middle of the three compartment cell, separated by two immobilized (enzyme) membranes, was utilized to feed lactose solution; whereas, adjacent compartments were filled with distilled water. The reacted mixture solution was analyzed for tri-, tetra- and penta-forms of GOS. The formation of product GOS strongly depended on varying amounts of initial lactose concentration (ILC). Total GOS formation increased from 7% to 28% for ILC from 50 to 200 g/L. However, tri-saccharide was the major (67%) in comparison to tetra (27%) and penta (6%) forms of GOS. Further, based on Michaelis-Menten kinetics, a six-step-eleven-parameter model was developed. The model incorporated enzyme inhibition and formation of glucose and galactose separately. Simulated results from developed model matched exceeding well with experimental results. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.