Zeolite beta particles with different sizes and narrow size distribution were hydrothermally synthesized and incorporated into chitosan (CS) matrix to prepare CS/zeolite beta hybrid membranes for direct methanol fuel cell (DMFC). It was found that the chitosan membrane filled by zeolite beta particles about 800nm in size exhibited the lowest methanol permeability, which can be ascribed to their optimum free volume and methanol diffusion characteristics. To further improve the performances of CS/zeolite beta hybrid membranes, zeolite beta particles about 800nm in size were sulfonated via three different approaches. The results indicated that the introduction Of sulfonic groups could reduce the methanol permeability further as a result of the enhanced interfacial interaction between zeolite beta and chitosan matrix. Furthermore, in terms of the overall selectivity index, CS/zeolite beta hybrid membranes were comparable to Nafion (R) 117 membrane at low methanol concentration (2 mol L-1) and much better at high methanol concentration (12 mol L-1). (C) 2008 Elsevier B.V. All rightS reserved.