Transport, thermal and structural properties of (1 - x)CsHSO4-xSiO(2) (where x = 0-0.9) composite solid electrolytes have been studied by complex impedance, DSC and X-ray diffraction methods. The used highly dispersed silica are different in their specific surface area (13-580 m(2)/g), pore size (R = 14-1000 Angstrom) and pore size distribution. It was shown that the low-temperature phase conductivity of composites is ca 2-2.5 orders of magnitude higher than that of the individual CsHSO4. Composite properties depend on content and pore size of SiO2. The low-temperature phase conductivity is maximum at x = 0.5-0.7. The optimum pore size of heterogeneous dopant is in a range of 35-100 Angstrom, where the most composite conductivity increase takes place and thermodynamic and structural properties change markedly ('dimensional effect'). For composites based on these silicas the enthalpies of CsHSO4 superionic phase transition and melting considerably decrease. As x increases the ionic component becomes either partially or completely amorphous. The CsHSO4 dispersion most likely proceeds in composites based on silica, the pore size of which is 170 Angstrom.