Sulfonated polyether ether ketone (SPEEK) is prepared by the sulfonation of polyether ether ketone (PEEK). Five of the composite membranes (PSW1-PSW5) with various percentage compositions of the SPEEK, PVAco-ethylene, and silicotungstic acid (SWA) were prepared. The prepared composite membranes were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Surface morphology of the composite membranes was analyzed using scanning electron microscopy (SEM). Other evaluations related to conductivities (ion exchange capacity, IEC), proton conductivity), absorptivity (water and methanol absorption), durability and mechanical properties (tensile strength and percentage elongation) were also evaluated for the composite membranes. Among the five composite membranes, composite membrane with higher SWA content, PSW5 (which has 10% SWA) showed more conductivity compared to other membranes. These composites also showed very good conductivities, mechanical properties, and durabilities. Hence, these composite membranes have the potential to be used in the development of newer proton exchange membrane fuel cells (PEMFCs). ©Springer Science+Business Media, LLC 2010.