NiO/MgO solid solution was prepared by heating a fixed amount of magnesium basic carbonate with increasing amounts of nickel nitrate followed by calcination at 1073 K. The mol fraction (MF) of NiO was varied between 0.053 and 0.333. The sample containing 0.25 MF NiO was doped with 2.5 and 5 mol% Li2O followed by calcination at 1073 K. The XRD patterns of various investigated solids were measured and different electric properties were investigated. These properties include: sigma, epsilon\, tan delta and the activation energy of electrical conductivity. The results showed that pure and variously doped solids consist of MgO phase while all the diffraction lines of NiO disappeared completely indicating the formation of NiO/MgO solid solution. The dissolution of 0.25 MF NiO resulted in a measurable increase in the lattice constant, a of MgO which decreased by increasing the amount of NiO above this limit, falling to values smaller than that measured for pure MgO. The ac and dc values of sigma were found to increase progressively by increasing the mol fraction of NiO and also by increasing the amount of Li2O added. The values of epsilon\ and tan delta were found to decrease progressively by increasing the NiO-content and also by increasing the frequency of ac current. However, the activation energy of a increased by increasing both the mol fraction and the amount of Li2O, which did not run parallel to the observed increase in the sigma values due to these treatments. This discrepancy had been attributed to a compensation effect of the pre-exponential factor of the electrical conductivity, sigma(0). The increase in a value due to increasing the MF value of NiO present was attributed to a significant increase in the concentration of the charge carriers without affecting their energetic nature (Ni2+, Ni3+). While the induced increase in a value of the investigated system due doping with Li2O resulted mainly from an effective increase in the mobility of the charge carriers present. (C) 2004 Elsevier B.V. All rights reserved.