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Among various NOx reduction technologies, selective catalytic reduction (SCR) methods have been studied for the cleaning of diesel engine exhaust. The urea SCR system, in which ammonia is used as a reducing agent, is thought to be one of the most promising methods. However, further improvement of the performance is required for low-temperature exhaust below 400 K. The purpose of this paper is the plasma reforming of solid urea to generate ammonia. In this paper, a dielectric-barrier-discharge plasma reactor in which dielectric pellets and urea powder were packed was experimentally investigated. The reactor was fed with humid gas and driven by pulsed high voltage at 400 K or lower. The effect of the pellet material, the gas humidity, and the gas flow rate were experimentally examined. The application of discharge plasma enhanced the ammonia production significantly. These results suggest that our method can provide a plasma-assisted solid-urea reforming system to generate ammonia.