As part of the development of poly(ether sulfone) (PES) membranes whose surface is modified by the incorporation of a newly synthesized hydrophobic surface modifying macromolecule (nSMM) additive, this study investigates the impact of four key membrane preparation factors. They are concentration of PES, concentration of nSMM, casting thickness, and casting speed. The synthesis and characterizations of nSMM by nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimeter, and elemental analysis have been presented. The changes in characteristics and performance of the membranes have been evaluated via Fourier transform infrared spectroscopy, contact angle analysis, scanning electron microscopy, and solute transport tests. The addition of 0.5 wt % of nSMM increased the contact angle of PES membranes by 20 degrees; however, higher nSMM concentrations did not increase the hydrophobicity any further. Only the additive concentration had a statistically significant impact on flux reduction and dissolved organic carbon rejection. Even though other factors such as membrane thickness may alter the pore characteristics, their effect on membrane performance was marginal. (c) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2626 -2637, 2010