CsHSO4 and dodecatungstophosphoric acid (H3PW12O40 center dot 6H(2)O:WPA center dot 6H4(2)O) were mechanically milled to synthesize xCsHSO(4)center dot(100-x)WPA (mol%) composites. H-1 NMR measurements suggested that a hydrogen bond was newly developed between WPA and CsHSO4, and proton transfer at CsHSO4-WPA composite region was considered to be faster than that at pure CsHSO4 or WPA. Proton conductivity of the 90CsHSO(4)center dot 10WPA (mol%) composite at 100 degrees C showed much higher of 3.3 x 10(-3) S/cm than that of pure CsHSO4 (4 x 10(-7) S/cm) or that of WPA(1 x 10(-7) S/cm). The -O(H)center dot center dot center dot O hydrogen bonding distance was estimated from the H-1-isotropic chemical shift of H-1 MAS NMR spectra. The proton conductivities in dry atmosphere of CsHSO4 center dot WPA composites were strongly correlated with the O(H)center dot center dot center dot O bond distance L. 2009 Elsevier B.V. All rights reserved.