The decomposition of trichloroethylene (TCE) in air by nonthermal plasma processing was studied as a function of excitation frequency, including combination effects of the nonthermal plasma with various catalysts. Two plasma reactors, a col type and a bolt type, were tested for frequency dependence. For TCE decomposition, 50-Hz excitation was the most efficient in energy among three frequencies: 50,500, and 2000 Hz. Greater ozone generation is found at 500 Hz than at 50 Hz, suggesting ozone does not play a dominant role in TCE decomposition. V2O5/TiO2 and Cu-ZSM-5 catalysts were effective in decomposing TCE, but cordierite catalyst did not work at all.