Alumina modified by MgO as the catalyst support loading Co3O4 for the N2O decomposition were investigated. It was found that MgAl2O4 was formed over the alumina surface by the MgO reacting with Al2O3 after calcination at 900 degrees C and using the composited support containing 30 wt% MgO loading Co3O4 can effectively suppress undesired CoAl2O4 formation under 700 degrees C. In the 20Co/30Mg-Al catalyst, it was found that about half of the cobalt is present as (Co,Mg)O solid solution and the rest exists as Co3O4, as characterized by Raman spectroscopy and H-2-TPR. The catalyst exhibited much higher and stable activity for the N2O decomposition compared with the 20Co/Al without MgO modification. [GRAPHICS] .