Composite solid electrolytes in the system (1-x)LiClO4-xAl(2)O(3) were prepared by sintering of preliminarily dehydrated components at 300 degrees C; their thermodynamic, electrical and electrochemical properties were investigated. Conductivity of pure anhydrous lithium perchlorate did not exceed 10(-5) S/cm. at 200 degrees C. Heterogeneous doping of LiClO4 by nanocrystalline gamma-Al2O3 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 similar to 10(-2) S/cm at 200 degrees C in vacuum. The electrochemical decomposition potential of LiClO4 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, Ph, Ag, Cu) in vacuum at 200 degrees 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. (c) 2006 Elsevier B.V. All rights reserved.