LnBaB(9)O(16) (Ln = Y, Gd) and europium-doped materials were synthesized by solid-state reactions. The electron and X-ray diffraction studies show that these compounds crystallize in the rhombohedral crystal system with the lattice constants a = 7.785(2), c = 46.21(1) Angstrom for YBaB9O16 and a = 7.809(2), c = 46.47(1) Angstrom for GdBaB9O16. The luminescent spectra of Eu3+-doped materials reveal that the local symmetry of the rare earth ions is centrosymmetric in YBaB9O16 and noncentrosymmetric in GdBaB9O16. The structures of these two compounds are similar and related by symmetry degradation, which occurs at about x = 0.1 in the Y1-xGdxBaB9O16 system.