The Co–Mn–Al mixed oxide catalysts on different supports (TiO₂, SBA-15, Al₂O₃, SiO₂, MMT, steel slag, granular blast furnace slag) were prepared by pore filling impregnation, characterized by AAS, XRD, SEM–EDAX, TPR-H₂ and N₂ physisorption and tested for N₂O catalytic decomposition in kinetic regime in an inert gas and in the presence of O₂, H₂O and NO. The catalytic properties were compared on the basis of specific activities ( ). The highest specific activities were observed over the Co–Mn–Al mixed oxide supported on SBA-15 and TiO₂ and the lowest on slags; the same trend was maintained in the presence of H₂O, O₂ and NO. The dependence of the specific activity on the catalyst reduction characteristics (amount of reducible species and easiness of reduction) was observed, which means that the tested supports affected the properties of the active components. Based on the values of the specific activities, the following order of the N₂O catalytic decomposition activity was found: Co–Mn–Al/SBA-15≈Co–Mn–Al/TiO₂≥Co–Mn–Al/MMT≈Co–Mn–Al/SiO₂>Co–Mn–Al/Al₂O₃≈Co–Mn–Al/S1≈Co–Mn–Al/S2.