The structure, microstructure, dielectric, and transport properties of the anion deficient perovskite solid solutions (La,Sr)(Ga,Mg,M)O3–δ with M=Fe, Ni have been studied. Substitution of iron and nickel for gallium up to about 20 and 40 at.% respectively, leads to the perovskite lattice contraction due to the cation substitutions by the transition elements. The transition from pure ionic to mixed ionic-electronic conductivity was observed for both the systems studied. Both the enhancement of total conductivity and increasing in the thermal expansion coefficient values has been proved to correlate with the increasing amount of weakly bounded oxygen species in the Fe or Ni-doped ceramics. The oxygen ionic conductivity has been estimated from the kinetic experiments using the dc-conductivity and dilatometry methods under the condition of the stepwise change of the atmosphere from nitrogen to oxygen. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)