Catalytic N₂O decomposition has been studied over metal-substituted hexaaluminates with the general formula ABAl₁₁O₁₉, where A = La, Ba, and B = Mn, Fe, Ni. The materials were prepared by coprecipitation via the carbonate route followed by calcination at 1473 K for 10 h. Inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), transmission electron microscopy (TEM), and N₂ adsorption techniques were used to characterize the catalysts. The activity in direct N₂O decomposition was evaluated by means of temperature-programmed reaction and steady-state experiments. Fe- and Mn-containing hexaaluminates present the highest activities. The Ni-containing catalysts are significantly less active, comparable to the hexaaluminates without metal substitution. The catalytic activity was practically not influenced by the A cation (La or Ba) in the structure. The Fe- and Mn-substituted hexaaluminates exhibit high activity and stability for N₂O decomposition in mixtures simulating the outlet of the Pt-Rh gauzes in ammonia oxidation reactors, containing N₂O, NO, O₂, and H₂O. These materials are promising for high-temperature abatement of this powerful greenhouse gas in the chemical industry, particularly in nitric acid and caprolactam production.