Our paper discusses a combined approach to reduce NO_x and particulate matter (PM) emitted by medium- speed marine diesel engines using non-thermal plasma (NTP) reactors. The design of the employed reactor relies on dielectric barrier discharge consisting of 36 parallel electrode rods positioned as to allow for movement of gas stream through the assembly. The plasma was driven by a novel power supply based on a series-parallel resonance circuit topology, which permits high voltage and frequency operation. Early results from the implementation of the non-thermal plasma reactor in the exhaust duct of a test bench diesel engine demonstrate considerable improvement of gas composition and particulate matter emission at extremely low energy densities (up to 16 J/dm³). The conversion of PM to gaseous SOF and soot is investigated and confirms that removal rate of unbalanced PM increases with a reactor’s power. In addition, a partial oxidation of NO to higher nitride oxides (e.g. NO₂) is identified.