A plasma-catalytic combined reactor system was used to decompose volatile organic compounds. Metal oxide catalysts, as well as Pt-based catalyst, were employed in the studies. The plasma treatment alone leads to the formation of high concentration of byproducts. A Pt-based catalyst, combined with plasma reactor, was helpful in minimizing the byproduct formation. The plasma reactor significantly enhances the catalytic performance. Plasma reactor, combined with Pt-based catalyst, removed more than 90% of toluene. The Pt-based catalyst completely removed the CO produced by plasma reactor. In order to determine the mechanism of the plasma treatment, the plasma reactor was replaced by ozone reactor and the results were compared with plasma-catalytic reactor. It was found that ozone plays a significant role in enhancing the catalytic activity.