Differential scanning calorimetry (DSC) and impedance spectroscopy (IS) were used to study the phase equilibria and electrical conductivity of (1-x)KHSO4-xAl(2)O(3) composites in the concentration range x=0.0-0.5. Alumina with grain size of 10 mum and pore size of similar to6 nm was used. Upon adding alumina, the phase transitions of KESO4 at 185 and 198 degreesC (melting point), respectively, are shifted to higher temperatures and a new phase transition is observed at about 170 degreesC for samples with compositions xgreater than or equal to0.2. Moreover, the two intense peaks at higher temperatures emerge to only one peak at about 200 degreesC for samples with composition xgreater than or equal to0.4. On the other hand, the dc-conductivity of KHSO4 decreases sharply at 164 degreesC on the first heating run, but this jump is shifted to 146 degreesC on the subsequent cooling run and decreases in size on the successive thermal cyclings. The addition of Al2O3 suppresses this anomaly and a rapid increase in the conductivity is observed at about 170 degreesC which corresponds to the DSC peak at this temperature. The results are discussed in terms of the effects of adding Al2O3 on the thermal and electrical properties of KHSO4. (C) 2004 Elsevier B.V. All rights reserved.