Anti-fouling thin-layer hydrogel composite membranes based on polyethersulfone (PES) ultrafiltration (UF) membranes were synthesized by addition of the crosslinking agents N,N'-methylene bisacrylamide (MBAA) and pentaerythritol triallyl ether (PETAE) to the modifier solution of poly(ethylene glycol) 400 methacrylate (PEGMA) in water under variation of the UV irradiation intensity and dose. The resulting membrane properties were characterized by means of water permeability, degree of grafting (DG), modification depth and skin-layer cross-section structure (scanning electron microscopy; SEM) as well as sieving/rejection behavior via filtration of polyethylene glycol (PEG) and dextran mixtures with wide molecular weight distribution (MWD) in water, the latter as additional study to already performed experiments on protein rejection [1]. For better understanding of the obtained results, bulk hydrogels were also prepared and the degree of swelling (DS) was determined. The performed experiments showed that the used crosslinkers changed the hydrogel layer structure and properties, which significantly affected the sieving/rejection behavior of the composite membranes. Using test solutions with low fouling tendency facilitated the validation of the obtained data in comparison to the previously reported protein rejection results. It was shown that polyPEGMA/MBAA composite membranes exhibited higher solute rejection, while polyPEGMA/PETAE showed lower solute rejection compared to uncrosslinked polyPEGMA composite membranes prepared with the same UV irradiation dose. Increasing the amount of crosslinkers amplified these effects. Furthermore, a trade-off analysis between water permeability and molecular weight cut-off (MWCO) for virgin and composite membranes was done in order to evaluate the membrane performance improvement by the composite membranes. The obtained results showed that the prepared composite membranes exhibited better fluxes and selectivity compared to commercial membranes with analogous characteristics. (C) 2011 Elsevier B.V. All rights reserved.