In a nitrogen stream under an atmospheric condition, NOx decomposition was investigated using two discharge-plasma systems, such as a Dielectric Barrier Discharge (DBD) and Packed Bed Reactor (PBR). In the absence of oxygen, the decomposition in the former system started at input voltage of 1kV and showed 100% conversion at 1.5kV, whereas that in the latter system started at 2kV and showed 100% at 3.5kV. With the increase of O₂ concentration, the conversion rapidry decreased in the both reactors.