Magnetic field treated perfluorosulfonate ionomer (PFSI) membranes (M-PMs) with improved through-plane proton conductivity are facilely fabricated though solvent casting of PFSI/Fe3O4 nanocomposite dispersion without any third additive under magnetic field followed by discarding the Fe3O4 nanoparticles. In the PFSI/Fe3O4 nanocomposite membrane, Fe3O4 nanoparticles are clearly uniaxially aligned by magnetic field. Subsequently, M-PMs are obtained by removing Fe3O4 from the nanocomposite membranes to eliminate the negative effect of Fe3O4 on proton conducting. The effect of magnetic field treatment on M-PMs' performance is investigated by both in- and through-plane proton conductivity. The results demonstrate that the through-plane proton conductivity of the M-PMs prepared from PFSI/Fe3O4 nanocomposite membrane with optimized Fe3O4 content is enhanced, while the in-plane proton conductivity is reduced compared to the pristine PFSI membrane, which indicate through-plane anisotropic phenomenon of proton conducting in the membranes. Such magnetic field treated PFSI membranes exhibit good appropriateness for using in electrochemical applications, for example fuel cells. (C) 2012 Elsevier B.V. All rights reserved.