Polysulfone (PSf) is one of the extensively used materials to prepare asymmetric membranes that possess outstanding properties such as high chemical, thermal, and mechanical stability. However, PSf membranes are characterized by relatively high contact angle values (CAº) around 80º and often susceptible to fouling and related problems1. Amphiphilic copolymers of PSf were also widely used to improve the hydrophilicity of membranes. They provide enhanced stability and hydrophilicity by engaging to membrane matrix with hydrophobic segments2, 3. Many studies have been conducted to clarify the effects of PVP and PEG on the rheological and thermodynamic properties of phase inversion process. Effects of increasing molecular weight and dosage of hydrophilic additives on membrane formation process were investigated in detail4, 5. However, to the best of our knowledge no study has been carried out on the effect of the composition of PSf-g-PEGMA copolymers to the phase-inversion process and resulting membranes. Non-linear PEG derivatives are actually amphiphilic structures and hydrophilicity of macromonomers depends on the chain length of ethylene oxide units6. Therefore, compositional variations of the copolymers may induce significant changes in the membrane characteristics that affect fouling resistance and membrane permeability7. In this work, first the PSf-g-PEGMA copolymers were synthesized with constant ratio of PEGMA (73 wt%) using the macromonomers in various molecular weights (PEGMA300, PEGMA475, PEGMA1100) then blended with PSf to prepare UF membranes via phase inversion. The effect of composition on membrane characteristics was assessed by viscosity measurements, SEM analysis, water flux and solute rejection tests. Surface segregation behavior of copolymers was investigated through contact angle and ATR/FT-IR analysis. Results of this study may contribute to defining better strategies to obtain membranes with desired properties. 1.Li, L.; Yan, G. P.; Wu, J. Y., J Appl Polym Sci 2009, 111 (4), 1942-1946. 2.Park, J. Y.; Acar, M. H.; Akthakul, A.; Kuhlman, W.; Mayes, A. M., Biomaterials 2006, 27 (6), 856-865. 3.Wang, J. Y.; Xu, Y. Y.; Zhu, L. P.; Li, J. H.; Zhu, B. K., Polymer 2008, 49 (15), 3256-3264. 4.Ma, Y. X.; Shi, F. M.; Ma, J.; Wu, M. N.; Zhang, J.; Gao, C. J., Desal. 2011, 272 (1-3), 51-58. 5.Susanto, H.; Ulbricht, M., J Memb Sci 2009, 327 (1-2), 125-135. 6.Lutz, J. F., J Polym Sci A-Polym Chem 2008, 46 (11), 3459-3470. 7.Wischerhoff, E.; Uhlig, K.; Lankenau, A.; Borner, H. G.; Laschewsky, A.; Duschl, C.; Lutz, J. F., Angew Chem-Int Ed 2008, 47 (30), 5666-5668.