While developing new business systems and reengineering of already existing ones, many organizations use the Unified Modelling Language (UML) to design a system’s structure and describe system’s behaviour. In spite of describing system’s behaviour with the UML model, the model itself is static. UML does not provide a possibility of running the model and studying the system’s behaviour. In such a situation the necessity arises to simulate the UML model. To provide that possibility, the designed UML diagrams could be transformed into a simulation model to be run within a specialized simulation environment. The paper discusses a transformation of that kind using the Arena simulation environment.