An organic-inorganic hydrophilic polymer-oxide hybrid proton conducting membrane (PCM) is produced from a host organic polymer, a filler inorganic oxide, and a proton-source with a pKa less than about 5. Usually, the subject invention comprises PCMs containing host polymer-x-strong acid-y-filler oxide, wherein x is between about 1 and about 10 (with "x" as the molar ratio of acid anion to polymer repeat unit) and y.ltoreq.about 50% (with "y" the weight percentage of filler oxide in the composite).