Dodecatungstophosphoric acid (H3PW12O40-nH(2)O) and SiO2 were mechanically milled, and a new class of proton-conductive composites was prepared. The conductivity of WPA-SiO2 Composite with P/Si=0.1 was 3 x 10(-3) S cm-' at 30 degrees C and 60% relative humidity (RH), which was higher than that (6 x 10(-4) S cm(-1)) of the corresponding mixture before milling. In the medium temperature range, the WPA-SiO2 composite retained relatively high conductivity of 1 x 10(-4) S cm(-1) at 100 degrees C and 2% RH, which was higher by one order of magnitude than that of the mixture without milling. These higher values of conductivity for the milled composite can be ascribed to the presence of mechanochemically formo,d surface defects such as Si-OH and P-OH groups. (c) 2007 Elsevier B.V All rights reserved.