The paper discusses the actual problem of NOx emission in real driving conditions. In the first part of the paper the existing situation in regard to the NOx emission of light vehicles in real use is presented using the tests performed all around Europe. Since the obtained emission is several times higher than existing limits according EU standards, the main causes for such differences have been analysed. Special attention is paid at the use of defeat devices applied by many car manufacturers using certain emission control strategy at approval test to obtain low emissions and another control strategy in real driving to obtain good fuel economy. To prevent excessive emission in real use, EU Commission has undertaken regulatory measures to accept new regulation which defines new limits for NOx emission in real use as well as control testing the light vehicles in real driving conditions.