Electric conductions in La0.9Sr0.1Ga1-xMgxO3-delta (LSGM; x=0 and 0.1) have been elucidated by ac and do methods as a function of temperature. Using complex-plane impedance analyses and dielectric relaxation processes along with do results, activation energy for electric conduction, migration energy of O2- ions (E-M), and energy required to create a free mobile oxygen vacancy which assists O2- migration (E-O) within intragrains and in boundaries have been obtained separately. Dielectric dispersion due to a distribution of relaxation times in boundaries is observed. The activation energy for each electric conduction is nearly equal to sum of E-M and E-O. Lattice distortion due to a large difference in ionic radii of Mg2+ and Ga3+ brings about high migration energy within intragrains in x=0.1 specimen compared with that of x=0. Such high migration energy has an adverse effect on improvement of ionic conductivities but excess oxygen vacancies compensate this adverse effect. In boundaries, disturbances in coulombic potential fields due to disordered ionic arrangements discourage ionic conductions. (C) 2004 Elsevier B.V. All rights reserved.