Stringent emissions standards (Euro 6 and Tier2Bin5) lead to the use of nitrogen oxides (NOx) after treatment. One of the most widespread technical solutions able to meet these legislations is Urea Selective Catalytic Reduction (Urea SCR). A urea aqueous solution is introduced into the exhaust system in order to reduce NOx over SCR catalyst. Before reaching the catalyst, the aqueous solution has to be transformed into ammonia. Current serial applications need long distances (>400 mm) from injection point to SCR catalyst and a mixer apparatus to ensure sufficient mixing between exhaust gas and ammonia. Because of this distance, SCR catalyst is located far from the engine. The light-off of the catalyst is penalized and therefore the efficiency of the SCR system is low. The purpose of this paper is to show a compact mixing device able to ensure mixing in a short distance (~75mm). Thanks to this compact mixer so called BlueBox, systems like SCR catalyst or two-way SCR/diesel particulate filter (DPF) catalyst in a close coupled position can be considered.