Effect of gas temperature on NOx removal by using dielectric barrier discharge (DBD) was investigated experimentally. NO/O₂/N₂ system was used as the test gas. The initial NO concentration was set as 100ppm. The experiment was conducted under two conditions with and without oxygen. The gas temperature was changed in a range of T_g=20°C～260°C. As the result, in the case of NO removal in nitrogen atmosphere (O₂=0%), NO was mainly reduced by N radical and several ppm of NO₂ and N₂O were produced. NOx removal efficiency at T_g=20°C (room temperature) was slightly higher than that at T_g=60～260°C. On the other hand, in the case of NOx removal in oxidative atmosphere (O₂=10%), NO was mainly oxidized by O₃ and reduced by N radical at T_g=20°C. At higher gas temperature conditions (T_g=60～260°C), NO_X concentration exceeded the initial NO concentration of 100ppm. The oxidation of NO with O₃ was controlled because the amount of O₃ was deceased due to the thermal decomposition of O₃. Also, NO, NO₂ and N₂O were produced by corona discharge in oxidative atmosphere. Thus, it was considered that the increase of NO_X in high temperature condition was caused by the thermal decomposition of O₃ and the formation of NO, NO₂ and N₂O.