Present work primarily deals with an exhaustive investigation on the effect of beta-galactosidase (EC 3.2.1.23) immobilization on polymeric polyether sulfone, cellulose triacetate and thin film composite polyamide membrane to produce galacto-oligosaccharides from lactose. Fouling is one of the key issues that control any membrane separation process to obtain the desired product. Especially, this issue with membrane becomes multiplied after making any attachment of immobilization chemicals on its surface, i.e. in case of enzymatic membrane reactor. Present work thus aims to identify the insights of carbohydrate interactions with the membrane surface after immobilization and how far it controls the production of galacto-oligosaccharides in this membrane reactor. (C) 2011 Elsevier B.V. All rights reserved.