Anion exchange membranes with high ionic conductivity and dimensional stability attract a lot of research interests. In present study, a series of fluorene-containing poly(arylene ether sulfone)s containing imidazolium on the flexible long side-chain are synthesized via copolycondensation, Friedel-Crafts reaction, ketone reduction, and Menshutkin reaction sequentially. The membranes used for characterization and membrane electrode assembly are obtained by solution casting and ion exchange thereafter. The morphology of the membranes is studied via transmission electron microscopy, and the microphase separation is observed. The long side-chain structure is responsible for the distinct hydrophilic-hydrophobic microphase separation, which facilitates the transport of hydroxide ions in the membranes. The incorporation of imidazolium on the flexible long side-chain is favorable for the ionic aggregation and transport in the membranes. The resulted membranes exhibit high hydroxide conductivities in the range of 48.5-83.1 mS cm(-1) at 80 degrees C. All these membranes show good dimensional stability and thermal stability. The single cell performance shows a power density of 102.3 mW cm(-2) at 60 degrees C using membrane electrode assembly based-on one of the synthesized polymers. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.