Composite solid electrolyes with enhanced conductivity have been mechanochemically prepared in Li2SO4-Al2O3 systems. The composites x=0.1-0.7 have been investigated. The highest conductivity 1.8×10-2 Sm/cm at 500°C with activation energy=0.59±0.04 eV has been observed for the solid electrolyte Li2SO4 - 50m/o Al2O3. Unusual dependence of conductivity on γ-Al2O3 content has been noted.