A new process for surface selective graft modification of ultrafiltration (UF) membranes with protective hydrogel layers was developed. The process uses a random copolymer of n-butylmethacrylate and N, N-dimethylaminoethylmethacrylate as a redox co-initiator ("macro-initiator"). Due to its molecular weight, the macro-initiator is completely rejected by the used Multibore (R) polyethersulfone UF membranes. Zwitterionic [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl) ammonium hydroxide and bifunctional N,N'-methylenebis(acrylamide) were used as monomers for "macro-initiator"-mediated, surface selective cross-linking polymerization toward anti-fouling hydrogel layers. The functionalization comprises two main steps; i) adsorption of the macro-initiator to the barrier layer surface of the membrane, e.g. during a short ultrafiltration; ii) grafting of the hydrogel layer after bringing the membrane in contact with a solution containing monomer(s) and a dissolved initiator (here ammonium persulfate) which is complementary to the co-initiator for a predetermined reaction time at room temperature. Hydrogel-grafted flat sheet and capillary UF membranes showed dextran sieving curves shifted to lower molecular weight values, increased total organic carbon rejection and improved antifouling behaviour in filtration tests with flower soil extract as model foulant. Furthermore, stability tests with sodium hydroxide and hydrogen peroxide solutions showed good chemical stability of graftfunctionalized membranes. The obtained results are very promising for future applications, since the presented technique can be applied in ready-to-use membrane modules and capillary membranes easily. (C) 2016 Elsevier B.V. All rights reserved.