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Perovskite ceramic samples of bulk La0.7Sr0.3MnO3 doped with Eu are prepared by usual thermal decomposition and grinding procedure. Besides La0.7Sr0.3MnO3 rhombohedral phase, with the substitution of Eu3+ for La3+, another perovskite-based structure with orthorhombic symmetry and space group Pnma can be identified by means of electron diffraction patterns (EDP) and energy-dispersive X-ray spectroscopy (EDX). Many 120 degrees large-angle orientation domains with a three-fold rotational symmetry relationship are observed in the orthorhombic grain. According to group theory of phase transformation and matrix analyses, the 120 degrees orientation domain originates from the three-fold symmetry axis of pseudo-cubic parent phase. Meanwhile, a projected model of the domain boundary is constructed based on their orientation relationships. The distortions and arrangements of MnO6, octahedra on the domain boundary are discussed particularly. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.