Effective reduction and removal of NOx from gas streams by dielectric barrier discharge (DBD) was studied. A laboratory-scale experimental system was designed and constructed to evaluate the removal efficiency of NO and NOx. Particularly, C2H2 was added as a reducing agent in the DeNOx plasma process via DBD. Experimental results indicated that the removal efficiency of NO/NOx increased with increasing applied voltage, gas temperature, and H2O(g) content. As the oxygen content in the gas stream is increased, more CHi radicals will be further oxidized to CO2, thus reducing the removal efficiency of NOx. When sufficient C2H2 was added to the DBD process, as high as 91.2% of NO and 68.2% of NOx were removed at 140°C for the gas stream containing 500 ppm NO, 1,500 ppm C2H2, 3.2% H2O(g), and 5% O2, with N2 as the carrier gas. In addition to N2 and H2O, the major products found in this process included NO2, N2O, HNO3, CO2, CO, and HCOOH, depending on H2O(g) and O2 contents of the gas stream.