A plasma-assisted hydrocarbon selective catalytic reduction (HC-SCR) system was constructed and its de-NOx performance was evaluated. An onboard plasma reformer supplied the reducing agent in the system. The reformate gas composition can be varied or the H(2)/HC ratio can be controlled by controlling the operating conditions. This ratio is important in the SCR process since the performance of the SCR catalyst is dependent on the composition of the reducing agents. Two catalysts were prepared for the test: those having lower-temperature and higher-temperature windows of operation. The proposed system showed a much enhanced de-NOx performance. Onboard plasma reforming enabled achievement of an enhanced de-NOx performance using about half the typical catalyst volume. Fuel penalty of the system remained at similar to 3%, with a possibility of further reduction without severe performance degradation. The system volume and power consumption also satisfy conditions necessary for its commercial application. Therefore, it appears suitable for commercial application. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights eserved.