Oxidation experiments in air from 775 K to 1145 K have established that at temperatures of 975 K and above, the peritectoid Ll2 phase, Zr3Al, under the influence of oxygen and nitrogen, undergoes the reverse peritectoid transformation Zr3Al → Zr2Al + Zr. This decomposition results in the formation of a lamellar Zr2Al/Zr product beneath the exposed surface. Correspondingly, the shortterm oxidation rate decreases and the oxide film becomes more adherent. The change in character is caused, at least in part, by the preferential oxidation of the αZr phase within the lamellar product, which leads to oxide platelets being held between the unoxidized Zr2Al lamellae.