So as to remove nitrogen oxides (NOx) using wet reduction technique, nitric oxide (NO) having low solubility in water should be converted into NO2. The injection of ozone, produced by dielectric barrier discharge plasma, into the exhaust gas gives rise to a rapid oxidation of NO that is the main component of NOx in most practical exhaust gases. Once NO is converted into NO2, it can readily be reduced to N2 in the next step by a reducing agent solution. Sodium sulfide used as the reducing agent in this study is ultimately converted into sodium sulfate, which is a nontoxic water-soluble compound. The present two-stage NOx removal process was able to remove about 95% of the NOx, initially contained in the simulated exhaust gas. The formation of H2S from sodium sulfide was prevented by using a strong basic reagent (NaOH) together with the reducing agent. The analyses of the reducing agent solution after processing show that about 80% of the NOx removed was reduced to N2 and the rest was simply dissolved in the form of NO2-or NO3-