A composite membrane of silica (SiO2)/sulfonated poly (ether ether ketone) (SPEEK) nanofiber mat impregnated with Nafion was fabricated and evaluated for its potential use as a proton conductor for high temperature polymer electrolyte membrane fuel cells. The supporting SiO2/SPEEK composite nanofibrous skeleton was prepared via electrospinning of a mixture of SPEEK solution and silica sol prepared from tetraethyl orthosilicate (TEOS). The control of hydrolysis and condensation of TEOS enabled to form entangled SiO2 networks miscible to SPEEK solution. The prepared SiO2/SPEEK nanofiber mat was impregnated with Nafion(A (R)) to completely fill the inter-fiber voids to prepare a dense membrane. The morphology of the nanofiber mat and the composite membrane were observed by scanning electron microscopy and the presence of SiO2 and SPEEK in the prepared nanofibers was confirmed by FTIR spectroscopy. Proton conductivity and swelling of the membrane were measured. The H-2/O-2 single cell test using the composite membrane as a PEM was performed. At a high temperature and low humidity condition (120 A degrees C and 40 % RH), the maximum power density was 170 mW/cm(2) for the Nafion-impregnated SiO2/SPEEK (40/60 w/w) composite nanofiber membrane that was 2.4 times higher than recast Nafion (71 mW/cm(2)) while SPEEK film failed.