Abstract: A series of Mg_xFe_1-xFe₂O₄ spinel oxides were prepared and characterized by means of nitrogen physisorption, X-ray diffraction (XRD) and temperature-programmed reduction of hydrogen (H₂-TPR). The effect of composition, calcination temperature, and potassium doping on the catalytic activity of the Mg-Fe mixed oxides in N₂O decomposition was investigated. The results indicated that the Mg_0.6Fe_0.4Fe₂O₄ catalyst calcined at 500 ℃ exhibits highest activity in N₂O decomposition. Unexpectedly, the catalyst activity is depressed by the addition of potassium, as the potassium doping may inhibit the reduction of surface iron oxides and reduce the surface area of K-modified catalysts. Long-term tests at 500 ℃ for 10 h also illustrate that Mg_0.6Fe_0.4Fe₂O₄ is superior to FeO_x catalyst either in the oxygen-alone or in the oxygen-steam concomitant atmosphere.