Perfluorinated sulfonic acid (PFSA)ionomersare representative proton-conductive polymer electrolyte materials with excellent chemical resistance. PFSA ionomers exhibitrelatively well-defined morphologies composed ofhydrophilic and hydrophobic moieties, which provide pathway and barrier for fast proton conduction and hydrogen permeation, respectively. A general way to change thedegree of hydrophilic-hydrophobic phase separation is thermal treatment at certain temperatures, particularly their glass transition temperatures. In this study, a simple way to transform their morphologies and to give improved proton conduction and reduced hydrogen permeationis suggested.