Atomistic simulations have been carried to investigate electric field induced transport of hydronium tons in a sulfonated poly(styrene co-divinylbenzene) membrane In order to provide a good description of this cross linked material, a methodology has been explicitly designed to construct a reliable model of the hydrated membrane This model has been used to carry out molecular dynamics simulations in presence of electric fields, which varied from 0 001 to 3 0 V nm(-1) Results show that the electric field affects the structure of the membrane producing both a redistribution of the unoccupied volume, which modifies the heterogeneity of the resin and a rearrangement of the negatively charged sulfonate groups which undergo a systematic alignment along the electric field direction As was expected, the mobility of hydronium ions is enhanced with the strength of the electric field Moreover the electric field induces a significant rearrangement of the sulfonate groups, which is evidenced by the alignment of the C-S bonds along the direction of the field The membrane has been found to behave as a spring, in which the force exerted by the electric field acts in opposite sense to the force exerted by the Internal structure of the cross-linked material