Facile synthesis of poly (ether sulfone)-based anion exchange membranes (AEMs) bearing flexible pendent quaternary ammonium (QA) groups for fuel cells is reported. (2,3-Epoxypropyl) trimethyl ammonium chloride (EPTMAC) is directly grafted onto the hydroxyl-bearing poly (ether sulfone) (PES) backbone via one-step ring-opening reaction to introduce ion conductive moieties. This scheme is more straightforward than the conventional two-step functionalization approach via chloromethylation or radical-initiated bromination and Menshutkin reactions. This method can be used to control the degree of functionalization of QA-containing PES easily. 2D nuclear overhauser effect spectroscopy (NOESY) shows that QA groups aggregate and self-assemble in the functionalized-PES solutions which are in favor of fabricating a membrane with phase separation morphology, as well as confirmed by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). These resulting AEMs exhibit reasonable hydroxide conductivity, low water uptake, high power density, and desirable durability in a single fuel cell. This suggests that they are good candidates for fuel cells. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.