In this study, (Mg, Al)-doped apatite-type lanthanum germanates were studied as a potential electrolyte for ITSOFC. La10-xMgxGe5.5Al0.5O26.75-x/2 (x = 1.0, 0.6, 0.4, 0.2) were synthesized by solid state reaction. The phases of samples were determined by X-ray powder diffraction data using the Rietveld refinement and the lattice volumes increase with Mg doping amount. The conductivities obviously increase with Mg content below 600 degrees C measured by impedance spectroscopy. The mechanism of oxygen ion migration is discussed. (c) 2008 Elsevier B.V. All rights reserved.