The electrical properties were studied of a series of cobalt-substituted lithium ferrites. We have found that all the samples studied have single phase of spinel structure. The lattice constant and the density increase with increasing Co 2+ contents. All the specimens studied have two regions of different activation energies. In the region below Ta (220°C) the conduction is attributed to electron hopping from Fe 2+ to Fe 3+ and in the region above Ta it is attributed to Li ion. The change of mobility is caused by the dispersion of ions.