Proton conductivity measurement and ac impedance analysis of CsHSO4/SiO2 composites were carried out using two different methods to prepare sample powders: mechanical mixing and evaporation to dryness. At temperatures below the superprotonic phase transition temperature of CsHSO4, ca. 140degreesC, the conductivity of the composite prepared by the evaporation to dryness method was larger by 4 orders of magnitude than that of pure CsHSO4, and larger by 2 orders of magnitude than that of the particles (2-16 nm) influenced the conductivity, with the composite prepared by mechanical mixing. The pore size of SiO2 conductivity becoming higher as the pore size became larger. In the impedance spectra, two semicircles appeared in the composite system and were deconstructed to study proton conduction processes. Impedance analysis suggests that the formation of an interface between CsHSO4 and SiO2 and the high dispersion of SiO2 particles result in the enhancement of conductivity. X-ray diffraction and differential thermal analysis indicate that structural disorder in the interface would induce a significant enhancement of conductivity even at temperatures below the phase transition temperature. (C) 2004 The Electrochemical Society.