A corona-discharge reactor was applied to remove benzene and p-dichlorobenzene from nitrogen and a nitrogen-oxygen mixture. Although benzene was not effectively removed from nitrogen by electron attachment, the removal efficiency was improved greatly by mixing oxygen. On the other hand, the high removal efficiencies of p-dichlorobenzene were obtained in nitrogen or a nitrogen-oxygen mixture. The removal mechanism was studied based on the contribution of the ozone reaction and the analysis of the deposit on the anode of the reactor. As a result, the ozone reaction does not contribute to the removals. An FT-IR measurement and thermogravimetry suggest that benzene or p-dichlorobenzene is decomposed by dissociative electron attachment and deposits as polycyclic aromatic compounds of a high boiling point on the anode surface.