Bis(phenyltrimethylammonium) calcium tetraazide is formed by the reaction of phenyltrimethylammonium azide with calcium azide in aqueous solution. The structure of the title compound was determined by single crystal X ray diffraction. The crystals are monoclinic, a = 9.713(2) A, b = 9.742(3) A, c = 13.145(4) A, β= 92.24(1)°, space group P21/a, Z = 2. The structure was solved by direct methods and refined to a conventional Rw= 0.059 for 1328 independent MoKα counter reflections. Calcium is octahedrally coordinated to six nitrogen atoms of different azide groups. The octahedra are connected via azide groups to form condensed monolayers in the a/b plane. The complex cations are arranged between these layers.