The composite solid electrolytes (1 - x)MeHSO4-xSiO(2), (where Me = Cs, Rb, x = 0-0.8) have been studied by complex impedance, DSC and X-ray diffraction methods. The used SiO2 varied in specific surface areas (13-580 m(2)g(-1)), pores size (R = 14-1000 Angstrom) and pores size distribution. The low-temperature conductivity of the composites was shown to exceed by 1-3 orders of magnitude that of the individual salts. It depended on SiO2 content, silica pores size and their distribution. There is optimum silica pores size in a range of 35-100 Angstrom, where the most composite conductivity increase takes place; the ionic component becomes either partially or completely amorphous with x increasing ("dimensional effect"). The MeHSO4 dispergation mainly proceeds in composites with R = 170 Angstrom. The MeHSO4 state does not change when the SiO2 pores size is 1000 Angstrom. In systems with R = 14 Angstrom both MeHSO4 low-temperature phase and amorphous state are observed.