Reduction of nitric oxides in the exhaust of Diesel-engines by urea-SCR is a well known technique for stationary operating engines. Conversion rates of up to 99 % are possible without slip of ammonia. However the application of urea-SCR for vehicles like trucks or passenger cars fitted with Diesel-engines requires additional information about the dynamic behaviour of different system components under various conditions of exhaust-gas temperature, space velocity and NOx-concentration level. This paper presents results of investigations sponsored by a research organization of the German industry, FVV (Forschungsvereinigung Verbrennungskraftmaschinen e.V.. Frankfurt). The results indicate that NOx-conversion is mainly dependant on exhaust-gas temperature, feed α (it means the mole number of ammonia farmed from urea addition related to the total mole number of nitric-oxides) and finally the space velocity. Conversion rates of up to 90% have been obtained at stationary engine conditions and more than 70% at dynamic engine operation starting with cold engine.