A method for the preparation of highly conductive and stable organic -inorganic nanocomposite polyelectrolyte membranes with controlled spacing between inorganic segment and covalently bound sulfonic acid functional groups has been established. These polyelectrolyte membranes were prepared by condensation polymerization of the silica precursor (tetraethylorthosilicate) in dimethylacetamide in the presence of poly(ethylene glycol) (PEG) of desired molecular weight, and sulfonated poly(styrene-co-maleic anhydride) was attached to the polymeric backbone by hydrogen bonding. Molecular weight of PEG has been systematically changed to control the nanostructure of the developed polymer matrix for studying the effects of molecular structure on the thermal as well as conductive properties. These polyelectrolyte membranes were extensively characterized by studying their thermo-gravimetric analysis (TGA), ion-exchange capacity (IEC), water content, conductivity, methanol permeability, and current-voltage polarization curves under direct methanol fuel cell (DMFC) operating conditions as a function of silica content and molecular weight of PEG used for membrane preparation. Moreover, from these studies and estimation of selectivity parameter among all synthesized membranes, 30% silica content and 400 Da molecular weight of PEG resulted in the best nanocomposite polyelectrolyte. membranes, which exhibited performance comparable to that of the Nafion 117 membrane for DMFC applications.