Organic-inorganic membranes for direct methanol fuel cell (DMFC) application were prepared from sulfonated polyether ether ketone (SPEEK), containing heteropolyacids and an oxide phase either generated by hydrolysis ofamino-modified silanes or by dispersion of a surface-modified fumed silica. The heteropolyacid was based on lacunary divacant [gamma-SiW10O36](8-) and contained epoxy groups which reacted with the amino-groups in the oxide phase. The reaction provides a covalent bond between the heteropolyacid to the insoluble oxide phase, resulting in its fixation in the membrane. The organic-inorganic composites prepared in this way were more stable than the plain membrane, had lower methanol crossover and proton-conductivity in the same order of magnitude.