The behavior of ammonia absorption and desorption was studied for CaCl2-CaBr2 halide mixtures with various molar ratios prepared via the aqueous solution method. The CaCl2-CaBr2 halide mixture was revealed to form solid solutions in any molar contents. Ammonia absorption abruptly increased at some pressure, forming the ammine complex, and the (step) pressures were different for the samples with different molar contents. The step pressure decreased when the Cl/Br ratio was decreased for both absorption and desorption cycles. All samples absorbed ammonia irreversibly, up to two molecules of ammonia coordination. Three samples-CaCl1.33Br0.67, CaClBr, and CaCl0.67Br1.33-proved to separate a great deal of ammonia at pressures of 60-10 kPa at 298 K. These samples are promising candidates for ammonia storage material to be used for pressure swing separation in a new ammonia synthesis process. Especially, CaCl1.33Br0.67 treated at 523 K showed the best separation capacity (27.1 mmol/g).