One of the political goals of the EU in broad is the absorption of all European continent state in a sort of United States of Europe. Nowadays the EU counts 28 states and the perspective of enlargement is not stopped by the current economic crisis. The current situation after the just completed pro-EU revolution in Ukraine and the implementation of strong economic link with former USSR Transcaucasian Republics (Georgia, Armenia and Azerbaijan) may suggest the final number of state in the EU. Many people believe that the United States of Europe puzzle is nearly full defined … but a new kind of EU enlargement may change the situation. This paper will focus only in one question. “Is an EU Member state secessionist territory automatically in the EU after archiving its Independence or have to reapply?” To answer to this question I will analyses the possible past experiences in secessionist territory getting membership in international organization like UN. The Vienna Convention on Succession of States in Respect of Treaties is a good material to use in case of succession but the fact that is not in force and not signed by the greatest part of EU member state make it only advisory and not binding.