This study is aimed to explain the challenges or obstacles that encountered by Western Balkans Countries; Albania, Montenegro, and North Macedonia in fulfilling Copenhagen criteria that set by European Union Enlargement Policy. These former ruled-communist countries have found it hard to get the full membership of European Union while the other two neighbors countries Slovenia and Croatia, have joined EU. In this research, the author used concept of Enlargement Policy and Copenhagen Criteria by Frank Schimmelfennig and Common and Foreign Security Policy (CFSP) to identify the obstacles. The researcher used qualitative analysis methods supported by secondary sources for the data analysis. This study found that Albania, Montenegro, and North Macedonia as former communist-ruled countries in taking transitional tasks on Copenhagen criteria from EU by adopting democratic values have hampered by high of corruption because of weak functions of democratic institutions and judicial system, in which still have to be fixed or reformed as well as to align its legislation with EU standards, especially with all EU common foreign and security policy positions and declarations in order to have EU full membership.