Toluene is one of the typical index substances of environmental odor. In this study the vaporized toluene was decomposed by peroxide ions which are formed from a newly developed low-temperature plasma generator. The number of ions composed mostly of negative was controlled by electric voltage below 3.0 kV, which could produce the minimum super oxide and ozone. The test plasma generator produced 84.1~560×103 ions/㎤ depending on air velocity. It was found that toluene decomposition rate corresponded proportionally to the plasma intensity. The efficiency with the plasma output, 3.0 kV was 97.5% in a batch process.