The (Gd,Eu)(2)O-3-Al2O3 system with the (Gd,Eu)(2)O-3/Al2O3 molar ratio between 0.6 and 1 was investigated. X-ray diffraction and high-resolution electron microscopy have revealed the perovskite, (Gd,Eu)AlO3, being the only stable phase, and no evidence of Al2O3-solubility in the perovskite phase. The Rietveld refinement on Gd0.95Eu0.05AlO3 has shown an orthorhombic GdFeO3-type structure (space group Pbnm), in which the AlO6 octahedra tilt along the primitive [100](p) and [110](p)-axis, respectively. Due to the tilting, the trivalent rare earth ions are surrounded by eight oxygen's only, and the symmetry changes from O-h to C-s. (C) 2004 Published by Elsevier Ltd.