The phenomenon of parallel structures or “a state within a state” is not new. The occurrence of the creation and operation of parallel institutions representing popular sovereignty is a socio-political phenomenon that accompanies transition societies. Such are considered societies emerging from colonization and those emerging from the process of revolutionary and evolutionary transformations of the communist system. However not all such structures that considers their activity to be parallel, are as such. Number of these structures appears to be illegal and their actions are considered to be illegal. With regard to the Serbian illegal structures operating in Republic of Kosovo, the withdrawal forced under NATO intervention of SerbYugoslav mechanisms of power from Kosovo in June 1999 marks the end of the war and at the same time the beginning of a new process of peace building. Despite the massive military and police withdrawal, members of the Serbian structures of security continued to reside in predominantly Serb enclaves, most of which began to reorganize, to defend the policy of S. Milosevic, whose regime continued to support the Serb strong line on staying in Kosovo by all means. However, these illegal structures do not represent majority of Serbs living in Kosovo, considering that this majority is incorporated into the constitutional institutions of the Rrepublic of Kosovo. This paper will scrutinize all of the aspects related to the illegal Serbian structures (supported also by the Government of Serbia) by showing why these structures are illegal and not parallel!