Ultrafiltration membranes were fabricated using blends of poly(ether sulfone) (PES) and PES modified with amine (-NH2) or amide (acetyl) groups on the aromatic ring. Amine groups were attached to the aromatic ring of PES through nitration and reduction reactions and acetylation of the amine groups was accomplished using acetic anhydride. The amine-modified polymers were analyzed with H-1 NMR and FTIR spectroscopy, to reveal that one -NH2 group was attached on each aromatic ring. Solutions of the polymers in DMF were coagulated in water to yield ultrafiltration membranes with a microporous skin and a macroporous support with macrovoids. The pure water permeances of the PES/PES-NH2 (amine-modified PES) and PES/PES-NHAc (amide modified PES) membranes made from solutions containing 10% unmodified PES and 6% modified PES were in between the PES membranes made from 10% to 16% PES solutions. This was attributed partly to the increased hydrophilicity due to the addition of modified PES and leaching of part of the modified PES during membrane preparation, which was verified through elemental analysis of the polymers and the membranes. The amine and amide groups on the membranes were chlorinated in hypochlorous acid solution to yield the antimicrobial N-halamines, which could be repeatedly applied after chlorine release by the membranes. Through iodometric titrations, it was found that the PES/PES-NHAc membranes could be chlorinated more than the PES/PES-NH2 membranes and remained chlorinated for a longer time upon exposure to flowing water. Antimicrobial activity tests using Gram-negative (Escherichia coli BL21) and Gram-positive (Bacillus subtilis) bacteria showed that both amine and amide modified membranes were successful in deactivating both types of bacteria. (C) 2016 Elsevier Ltd. All rights reserved.