Abstract Composite solid electrolytes in the system (1 − x )LiClO 4 – x Al 2 O 3 were prepared by sintering of preliminarily dehydrated components at 300 °C; their thermodynamic, electrical and electrochemical properties were investigated. Conductivity of pure anhydrous lithium perchlorate did not exceed 10 − 5 S/cm at 200 °C. Heterogeneous doping of LiClO 4 by nanocrystalline γ-Al 2 O 3 with specific surface area of 200 m 2 /g caused a substantial increase in conductivity. The conductivity of the composites goes through a maximum at the molar fraction of alumina around x = 0.4–0.5 and reaches the values of ∼ 10 − 2 S/cm at 200 °C in vacuum. The electrochemical decomposition potential of LiClO 4 in the composites, estimated from the analysis of volt–ampere characteristics of symmetric cells M/0.5LiClO 4 –0.5Al 2 O 3 /M (where M = Al, Ni, V, Pb, Ag, Cu) in vacuum at 200 °C, exceeds 4.5 V. It was suggested that the conductivity of the composites is governed by lithium ions; these solid electrolytes may be used in solid-state lithium batteries.