A novel polyelectrolyte complex (PEC) membrane for direct methanol fuel cells (DMFCs) was prepared by blending a cationic polyelectrolyte, chitosan (CS), with an anionic polyelectrolyte, acrylic acid-2-acrylamido-2-methylpropane sulfonic acid copolymer (P(AA-AMPS)). The presence of -NH3+ species detected by X-ray photoelectron spectroscopy (XPS) revealed that an ionic cross-linked interpenetrating polymer network (IPN) was formed between the two polyelectrolyte polymers. Methanol permeability and proton conductivity were measured and compared with the Nafion (R) 117 membrane. The dual function of P(AA-AMPS) as both an ionic crosslinker and a proton conductor led to not only a notable reduction in methanol permeability but also an increase in proton conductivity. The CS/P(AA-AMPS) membrane with a P(AA-AMPS) content of 41 wt.% exhibited a methanol permeability (P) of 2.41 x 10(-7) cm(2) s(-1) which was fifteen times lower than that of the Nafion (R) 117 membrane, whereas its proton conductivity (sigma) was comparatively high (3.59 x 10(-2) S cm(-1)). In terms of the overall selectivity index (beta = sigma/P), the PEC membrane showed a remarkably higher selectivity than the Nation (R) 117 membrane, and, furthermore, the overall selectivity index increased with the increase of P(AA-AMPS) content. The mechanism of proton transfer was tentatively discussed based on the activation energy of conductivity. (C) 2008 Elsevier B.V. All rights reserved.