Eu 2Mn 2/3Ta 4/3O 7 specimen was synthesized from Eu 2O 3, MnO and Ta 2O 5 in a reducing atmosphere. Structure analysis was carried out by Rietveld method from X-ray diffraction data. The X-ray diffraction profile calculated with monoclinic C2/c model was in a good agreement with the observed X-ray diffraction patterns since several small peaks of super lattice could be also assigned with C2/c symmetry in addition to fundamental reflection peaks. Eu 2Mn 2/3Ta 4/3O 7 has two kinds of distorted (Mn, Ta)O 6 octahedra and HTB layers, which deviates from the regular forms. Europium atoms coordinate to eight or seven oxygen atoms and lead to two kinds of polyhedra, EuO 8 and EuO 7 in this compound. Eu 2Mn 2 / 3Ta 4 / 3O 7 specimen was synthesized from Eu 2 O 3, MnO and Ta 2 O 5 in a reducing atmosphere. Structure analysis was carried out by Rietveld method from X-ray diffraction data. The X- monoclinic C2 / c model was in a good agreement with the observed X-ray diffraction patterns from several small peaks of super lattice could be also assigned with C2 / c symmetry in addition to fundamental reflection peaks. Eu 2Mn 2 / 3Ta 4 / 3O 7 There are two kinds of distorted (Mn, Ta) O 6 octahedra and HTB layers, which deviates from the regular forms. Europium atoms coordinate to eight or seven oxygen atoms and lead to two kinds of polyhedra, EuO 8 and EuO 7 in this compound.