(Mg1 -xFex)(1 - delta)O (x = 0.01-0.43) single crystals (similar to 8 mm in diameter) were made by a melt-growth method. Electrical conductivity measurements were carried out as functions of temperature and frequency by a complex impedance method under pressure (similar to 43 GPa and similar to 673 K and at 0.1 MPa and similar to 1400 K). Our experimental results show a change in charge transport mechanism in the (Mg1 - xFex)(1 - delta)O solid solution at high temperature. The temperature of inflection point of the slope in Arrhenius plots depend greatly on both composition and extrinsic factors of crystals. The low-temperature conduction mechanism in (Mg1 - xFex)(1 - delta)O solid solution is small polaron. Pressure effect of the electric conductivity was observed and the conductivity increased to 0.5 at log scale of S/m with increasing pressure up to 43.4 GPa. The activation energy was decreased linearly with increasing pressure. Chemical composition and homogeneity of specimen rather than pressure greatly influence the electric conductivity. The activation energy of 2.37(4) eV for the (Mg0.99Fe0.01)(1 - delta)O solid solution might correspond to a migration enthalpy of O ions through thermally formed defects. It is proposed that a possible dominant electrical conduction mechanism in ferroperidase under the lower mantle conditions, at least in the higher temperature region, is super ionic conduction. (C) 2008 Elsevier B.V. All rights reserved.