Low-temperature De-NOx technology is a new topic in the area of flue gas treatment. This paper presents experimental studies on selective catalytic reduction (SCR) of NOx from synthetic flue gas over iron-based catalysts with ammonia in a fluidized reactor. The iron-based catalysts used in the experiments are particles of Fe3O4 and gamma-Fe2O3, and they are analyzed by X-ray diffraction (XRD) and Mossbauer spectroscopy, before and after reaction. It is observed that the efficiency of De-NOx with gamma-Fe2O3 catalyst is high at temperatures from 200-290 degrees C and the maximum efficiency is seen to exceed 90 % at 250 degrees C. The effects of magnetic fields on SCR De-NOx using gamma-Fe2O3 particles as catalysts are also studied by applying uniform and coaxial magnetic fields to the fluidized bed. The results suggest that SCR De-NOx on gamma-Fe2O3 catalyst is fit for operation below 200 degrees C in the fluidized reactor in conjunction with the effects of magnetic fields.