Polymer-based materials with tunable nanoscale structures and associated microenvironments hold great promise as next-generation ion-exchange membranes (IEMs) for acid or alkaline fuel cells. Understanding the relationships between nanostructure, physical and chemical microenvironment, and ion-transport properties are critical to the rational design and development of IEMs. These matters are addressed here by discussing representative and important advances since 2011, with particular emphasis on aromatic-polymer-based nanostructured IEMs, which are broadly divided into nanostructured polymer membranes and nanostructured polymer-filler composite membranes. For each category of membrane, the core factors that influence the physical and chemical microenvironments of the ion nanochannels are summarized. In addition, a brief perspective on the possible future directions of nanostructured IEMs is presented. Polymer-based materials with tunable ion nanochannels hold great promise as next-generation ion-exchange membranes (IEMs) for acid or alkaline fuel cells. Using the physical and chemical microenvironments of ion nanochannels as the central pivots, an overview of nanostructured IEMs is presented, targeting at elucidating the relationships between nanostructures, microenvironments, and ion-transport properties.