The dc and ac conductivities of the mixed ferrite Li0.5-0.5xCuxFe2.5-0.5xO4 (where x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were studied in a wide range of temperature from 300 up to 720 K. Over this range of measurement, the ac conductivity seems to be independent of frequency at high temperature for all values of x. In the relatively low temperature region, the frequency dispersion is attributed to the hopping conduction of the localized carriers. The activation energy (E-sigma) in the dispersion region ranges from the lowest value of 0.24 eV to the highest value of 0.8 eV, while the average value of hopping energy (Deltaepsilon) was about 0.06 eV. Both dielectric constant epsilon' and dielectric loss epsilon" increase with increasing temperature. The dielectric behaviour is explained by using the mechanism of polarization process, which is correlated to that of electron exchange interaction. (C) 2003 Published by Elsevier B.V.