A mixed reality (MR) represents an environment composed both by real and virtual objects. MR applications are more and more used in different scientific and practical areas, for instance, in medicine, architecture, entertainment, manufacturing, etc. This paper describes development of mixed reality framework for visualization and execution of discrete event simulation models based on the Discrete Event System Specification (DEVS) formalism. The mixed reality framework provides a 3D augmented/virtual environment representing and executing simulation models that encapsulate the static and dynamic behavior of the simulated system. Basing on the DEVS formalism, there is also presented a new methodological concept, called Visual-DEVS (VDEVS).