The leading after-treatment technology for NOx removal process in Diesel engines for stationary and mobile applications is the selective catalytic reduction of oxides of nitrogen [NOx] by ammonia [NH3]. A novel non-thermal plasma electrode with a needle array in a dielectric barrier discharge reactor, powered by a high frequency neon transformer, is used for the thermal decomposition of solid urea [(NH2)CO(NH2)] to produce ammonia. The thermolysis of urea produces iso-cyanic acid [HNCO] as a byproduct, besides ammonia, which can react with water in the gas phase, thus giving carbon dioxide and more ammonia. The presence of water fed before and/or after the plasma reactor was studied to assess its effect on the amount of produced ammonia. Results clearly showed that water fed to the entrance of the reactor can efficiently promote the reaction of iso-cyanic acid to produce ammonia and this result can be improved when air is used as carrier gas for 115 V of input voltage to a neon transformer and with a gas flow rate of 4 L/min.