The intermetallic compound Mg2Al3 has been selected for this work to be tested as anode in a metal-air battery. The compound is prepared by a high-temperature synthesis from elements and its cubic structure (Fd 3¯¯¯ m, a = 28.2341(3) Å) has been refined from X-ray single crystal diffraction data. It is characterized by a high level of disorder with a large number of partially filled atomic sites, split positions, and atomic mixing. The compound displays an interesting behavior towards self-corrosion in alkaline and saline environments, but the better electrochemical performances are obtained in saline NaCl electrolyte. It is shown that both Al and Mg are involved in the oxidation reaction that occurs at the Mg2Al3 electrode used as anode in a metal-air battery. The operating voltage of an Mg2Al3-air cell is remarkably stable over several hours, and the Mg2Al3 anode efficiency is higher than that of a pure Mg anode in a saline environment.