Conversion of nitric oxide (NO) in a pulsed corona discharge reactor was investigated. Relative importance of each of the active species such as O, OH, HO2 and O-3 produced by corona discharge was evaluated with respect to the oxidation of NO to NO2. Of those species, O-3 was found to be the most important one in the oxidation of NO. In order to reduce the energy required to convert NO, olefins (ethylene, propylene) were used as additive, and the scheme for the oxidation of NO promoted by the hydrocarbon was discussed. In the presence of hydrocarbon, ozone also played very important role in the reaction mechanism. The concentration of ozone was measured at the reactor outlet to verify the importance of ozone in the oxidation chemistry. Compared to ethylene, propylene gave much better performance in the conversion of NO at the same specific energy. When propylene was added to the gas stream at identical amount to initial NOx (300 ppm), 60 % of NO could be converted with a specific energy of only 2.6 Wh m(-3).