The preparation and characterization of composite Nafion based membranes containing 5 wt.% and 10 wt.% of nano ammonium-X (NH4-X) (30-100 nm) and submicron NH4-X (200-300 nm) zeolites obtained by solvent casting are reported. Regardless of the filler size, the membranes with 10 wt.% loading of NH4-X zeolites show, on the surface in contact with mould, the formation of microcracking due to the segregation of filler aggregates whereas no defect is observed for the membranes with 5 wt.% loadings. The water uptake, the ion exchange capacity, and the proton conductivity of NH4-X/Nafion composite membranes are improved in comparison to pristine recast Nafion, The NH4-X/Nafion submicron 5 wt.% composite membrane has a selectivity that is more than twice that of pristine Nafion. Furthermore DMFC single cell tests showed that the peak power density exhibited by the NH4-X/Nafion submicron 5 wt.% composite membrane is 3 times higher than the value measured for pristine Nafion membrane at 60 degrees C. (C) 2015 Elsevier B.V. All rights reserved.