Various spatially enlarged organoclays were prepared by using poly(oxyproplene)-backboned quaternary ammonium salts of various molecular weights M-w 230, 400 and 2000 as the intercalating agents for Ne-montmorillonite. The modified MMT was utilized to improve the compatibility with Nafion (R). Sufficient interaction of the modified MMT with Nafiono was studied by using X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS). The performance of the Nafion (R)/m-MMT composite membranes for direct methanol fuel cell (DMFCs) was evaluated in terms of water uptake, ion exchange capacity (IEC), methanol permeability, proton conductivity, and cell performance. The methanol permeability of the composite membrane decreased with the increasing of rn-MMT content. The proton conductivity of the membrane was lowered slightly from that of pristine Nafiono membrane. These results led to an essential improvement in the single-cell performance of DMFCs. (c) 2007 Elsevier B.V. All rights reserved.