Sulfonated SiO2 nanoparticles with uniform core-shell structure are synthesized and used as functional fillers for preparing composite proton conducting membranes for direct methanol fuel cells (DMFCs). Poly(4-styrenesulfonic acid) in the shell of SiO2 nanoparticle contributes well-dispersion of the SiO2 nanoparticle in the Nafion membrane. The addition of core-shell SiO2 nanoparticles into Nafion matrix is very effective in improving membrane performance, including ion exchange capacity, proton conductivity, mechanical strength and methanol permeability. As a result, the DMFC assembled with a composite membrane exhibits superior performance as compared to a Nafion-based cell. (c) 2012 Elsevier B.V. All rights reserved.