The decomposition of benzene was carried out in two types of plasma reactors packed with BaTiO3 pellets: one reactor had two stainless steel electrodes (SUS reactor), and the other reactor had a glass layer between two concentric electrodes (GL reactor). The decomposition efficiency and the suppression of formation of N2O and NOx were greater in the GL reactor than in the SUS reactor. In contrast, the suppression of O-3 formation and the oxidation to COx in the SUS reactor were superior to those in the GL reactor. The effect of waveform and frequency of applied ac power was investigated for each reactor.