The NYAB powder with Nd composition was synthesized by solid-state reaction. Space groups for YAB and NAB were confirmed to be R32 and C2/c, respectively. Lattice parameters and decomposition temperature of NYAB, according to Nd concentration, were measured by X-ray diffraction and DTA. As the Nd content in NYAB was increased, the lattice constants were increased as well, but the decomposition temperature of NYAB was lowered. The space group of NYAB is R32 in the composition region of x = 0.0 similar to 0.8 and C2/c in the region of x = 0.81 similar to 1.0.