Organic/inorganic membranes based on sulfonated poly(vinyl alcohol) (s-PVA) and sulfonated multi-walled carbon nanotubes (s-MWNTs) nanocomposite membranes (SPVA) with various compositions were prepared for use as proton exchange membranes in direct membrane fuel cells (DMFCs). The SPVA membranes were cross-linked with both glutaraldehyde and s-MWNTs to reduce the level of water (methanol) uptake. The unreacted carboxylic acid and sulfonic acid of the s-MWNTs were also cross-linked with the hydroxyl groups of the PVA matrix. The ion exchange capacity (IEC) and proton conductivity of the membranes initially increased with increasing amount of s-MWNTs, because the s-MWNTs have abundant sulfonic acid groups. The composite membranes exhibited excellent proton conductivity ranging from 0.032 to 0.075 S/cm as well as low methanol permeability ranging from 1.12 x 10(-8) to 3.32 x 10(-9) cm(2) s(-1) at 60. (C) 2011 Elsevier B.V. All rights reserved.