Abstract: MgCo₂O₄ composite oxides with spinel structure were hydrothermally prepared at 120℃ by using carbon sphere as template and urea as precipitant. K₂CO₃ solution was impregnated on MgCo₂O₄ and the K-modified catalyst was obtained. These catalysts were applied in catalytic decomposition of N₂O and characterized by X-ray diffraction(XRD), nitrogen physisorption, scanning electron microscopy (SEM), temperature-programmed reduction of hydrogen (H₂-TPR), temperature-programmed desorption of oxygen (O₂-TPD), and X-ray photoelectron spectroscopy (XPS). Effect of catalysts preparation parameters such as mass ratio of cobalt and magnesium to carbon sphere, molar ratio of urea to metallic cations, on their catalytic activity was investigated. It is shown that the catalyst prepared with mass ratio 0.192 of cobalt and magnesium to carbon sphere, molar ratio 2 of urea to cobalt and magnesium cations, exhibits higher catalytic activity than others. Furthermore, 91% and 62% conversions of N₂O could be reached over 0.02 K/MgCo₂O₄ catalyst at 400℃ after continuous running for 50 h under the atmosphere of oxygen-alone and oxygen-steam together, respectively, revealing that K-modified MgCo₂O₄ catalyst is stable under both reaction atmospheres.