The purpose of this study to examine from a critical perspective the activities of the European Union which establish itself as an international political and security actor in Kosovo. Kosovo crisis has become an important issue not only for EU's Common Foreign and Security Policy but also for the operation of mision EULEX which established by EU as its most ambitious mission. The political process of solving Kosovo problem and the foreign policy interests of the union in this process and the linking of the process with the EU enlargement policy caused the intermingling of all processes and this has led to the issue more complicated. This complexity not only affected the legal and political status of the mission but also its achievements and the results. In this study, a critical evaluation of the EULEX mission has been carried out since its foundation. In this context, the conditions of the emergence, the legal basis, the structure of the mission and the effects of the mission's activities were examined and it was concluded that the EU's inclusion in the the solution of the Kosovo crisis with EULEX could not bring the expected success.