Abstract: A series of magnetic iron-magnesium mixed oxide catalysts (Fe1-xMgx Oz ,where x = 0,0. 1,0. 2,0. 3) were synthesized via a novel co-precipitation method with microwave thermal treatment and their activities were tested on a quartz fixed-bed reactor. Physical properties of the catalysts were characterized by X-ray diffraction ( XRD),N2 -ad- sorption-desorption,Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). Fe0. 8 Mg0. 2 Oz with a wide temperature window of 250 ℃ to 350 ℃ was validated as the proper SCR catalyst,and the maximum NOx conversion of 99. 1% was achieved at 325 ℃ . Activity was strongly influenced by the γ-Fe2 O3 crystalline phase,mag- nesium existed in an amorphous phase and interacted with iron oxide intensively to form solid solution. Optimum pore diameter distribution,appropriate surface area (44. 00 m2 / g),pore volume (0. 19 cm3 / g) and abundant lattice oxy- gen could be guaranteed in Fe0. 8 Mg0. 2 Oz catalyst,which was good for the diffusion process and enhanced the activity. The optimum O2 concentration of Fe0. 8 Mg0. 2 Oz catalyst was 3% ,and recommended NH3 / NO was 1. The improvement of oxidation ability on the surface of the catalyst and the rapid adsorption and activation of reactants were both in favor of NH3 -SCR reaction.