This study describes the modification of chitosan by introducing phosphonic acid group, which was confirmed by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (H-1 NMR) and preparation of its composite membranes with poly(vinyl alcohol) of different compositions. These membranes were extensively characterized for their morphology by scanning electron microscopy (SEM), thermal, mechanical and dimensional stability by thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and water uptake measurements at different temperatures. Different electrochemical properties such as ion-exchange capacity, proton transport number, proton conductivity, activation energy needed for the proton transfer, and methanol permeabilities of these membranes were also measured and compared with those Nafion 117 membrane. All these membranes exhibited comparable proton transport number and conductivity with Nafion 117 membrane, but quite lower methanol permeability compared to Nafion 117 renders their applications to direct methanol fuel cells (DMFC). Furthermore, selectivity parameters for DMFC of all the synthesized membranes are much higher in comparison to Nafion 117 membrane. (c) 2006 Elsevier B.V. All rights reserved.