Highly fouling-resistant ultrafiltration (UF) membranes were synthesized by heterogeneous photograft copolymn. of two water-sol. monomers, poly(ethylene glycol) methacrylate (PEGMA) and N,N-dimethyl-N-(2-methacryloyloxyethyl-N-(3-sulfopropyl)ammonium betaine (SPE), with and without cross-linker monomer N,N'-methylene bisacrylamide (MBAA), onto a polyethersulfone (PES) UF membrane. The characteristics, the stability, and the UF sepn. performance of the resulting composite membranes were evaluated in detail. The membranes were characterized with respect to membrane chem. (by ATR-IR spectroscopy and elemental anal.), surface wettability (by contact angle), surface charge (by zeta potential), surface morphol. (by SEM), and pure water permeability and rejection of macromol. test substances (including the \"cutoff\" value). The surface chem. and wettability of the composite membranes did not change after incubating in sodium hypochlorite soln. (typically used for cleaning UF membranes) for a period of 8 days. Changes in water permeability after static contact with solns. of a model protein (myoglobin) were used as a measure of fouling resistance, and the results suggest that PEGMA- and SPE-based composite membranes at a sufficient degree of graft modification showed much higher adsorptive fouling resistance than unmodified PES membranes of similar or larger nominal cutoff. This was confirmed in UF expts. with myoglobin solns. Similar results, namely, a very much improved fouling resistance due to the grafted thin polymer hydrogel layer, were also obtained in the UF evaluation using humic acid as another strong foulant. In some cases, the addn. of the cross-linker during modification could improve both permeate flux and solute rejection during UF. Overall, composite membranes prepd. with an \"old generation\" nonfouling material, PEGMA, showed better performance than composite membranes prepd. with a \"new generation\" one, the zwitterionic SPE.