An experimental study on the conversion of NO in the NO/N-2, NO/O-2/N-2, NO/C2H4/N-2 and NO/C2H4/O-2/N-2 systems has been carried out using dielectric barrier discharge (DBD) plasmas at atmospheric pressure. In the NO/N-2 system, NO decomposition to N-2 and O-2 is the dominating reaction; NO conversion to NO2 is less significant. O-2 produced from NO decomposition was detected by an on-line mass spectrometer. With the increase of NO initial concentration, the concentration of O-2 produced decreases at 298 K, but slightly increases at 523 K. In the NO/O-2/N-2 system, NO is mainly oxidized to NO2, but NO conversion becomes very low at 523 K and over 1.6% of O-2. In the NO/C2H4/N-2 system, NO is reduced to N-2 with about the same NO conversion as that in the NO/N-2 system but without NO2 formation. In the NO/C2H4/O-2/N-2 system, the oxidation of NO to NO2 is dramatically promoted. At 523 K, with the increase of the energy density, NO conversion increases rapidly first, and then almost stabilizes at 93-91% of NO conversion with 61-55% of NO2 selectivity in the energy density range of 317-550 J L(-1)supercript stop. It finally decreases gradually at high energy density. A negligible amount of N2O is formed in the above four systems. Of the four systems studied, NO conversion and NO2 selectivity of the NO/C2H4/O-2/N-2 system are the highest, and NO/O-2/C2H4/N-2 system has the lowest electrical energy consumption per NO molecule converted.