The formation of a continuous series of solid solutions with a rhombohedrally-distorted perovskite type structure has been found in the pseudobinary oxide system LaCoO3-LaGaO3. Substitution of gallium with cobalt in the lanthanum gallate results in blocking oxygen ionic transport and increasing electronic conductivity. The activation energy of the electrical conductivity of the LaGa1-xCoxO3 ceramics (x=0.2-0.6) is in the range 57-65 kJ mol(-1). The thermal expansion coefficients increase regularly with the cobalt content and lie in the range from 11.2 x 10(-6) to 22.3 x 10(-6) K-1. Doping LaCoO, with gallium has been ascertained to lead to lower electronic conductivity and oxygen permeability. The results of electrical conductivity and electron paramagnetic resonance (EPR) studies suggest that introduction of gallium into the cobalt sublattice leads to insulating cobalt ions.