Elimination of CO in air stream using the plasma catalytic reactors was investigated. Two plasma catalytic systems were evaluated in this study, one consisting of a catalyst-bed packed in plasma zone of a dielectric barrier discharge (DBD) reactor directly (CID reactor), and the other (CAD reactor) consisting of a catalyst-bed after a DBD reactor. The examined operating parameters in this study included applied voltage, discharge power, the lengths of plasma zone and catalyst-bed, and inlet CO concentration. It was found that the glass packed DBD reactor without catalyst cannot eliminate CO in air stream effectively. When MnOx catalyst applied to DBD reactors, the removal of 1000 ppm CO can achieve to 97% by both type reactors. Under constant energy input condition, the CO removal of a CID reactor increased with the decrease of the initial CO concentration and the increase of the length of catalyst beds. In addition, the operating energy consumption of CID system was lower than that of CAD system.