The family business Pongratz Trailer Group produces car trailers in Austria, in Traboch and in Slovakia in Modra. Due to the good order situation especially the capacity of the assembly in Modra is stretched to its limits. The management supposes that there is potential for improvements to reduce assembly times and raise output. In the course of an analysis both assembly plants should be inspected. The aim of this thesis is to record the assembly times and to optimize them. The time measurement of the processes, which was carried out by a modified procedure based on the time recording method REFA, has proved that in Modra above all the bad organisation and design of the workplaces as well as the material supply are responsible for unnecessary long assembly times. The present subdivision and arrangement of the assembly places as well as storage areas also offers space for improvements. In this thesis state-of-the-art methods are adjusted to the situation and solution approaches are developed. Kanban, 5S, a new concept of the material supply and a new layout should shorten the assembly times and raise the output. How and in which order these measures should be applied as well as the financial aspects of these effects are also part of this work. Theoretical backgrounds from the literature are combined with real circumstances from the practice. The solutions are adapted to the constellations on site and therefore they are realizable and good to implement.