The range of existence of Nd₂Sr_1-xCa _xAl₂O₇ solid solutions (x ≤ 0.5) was established. The distribution of neodymium, strontium, and calcium cations over two structural sites was studied by full-profile X-ray analysis. Unlike La ₂Sr_1-xCa_xAl₂O₇ solid solutions, Ca²⁺ cations fill not only nine-vertex AO₉ polyhedra, but also oxygen cubic octahedra AO₁₂. Introduction of calcium results in disordered distribution of Nd³⁺ cations, destabilization of the layered structure, and decomposition of the solid solutions.