The last decade has been a period of accelerated integration in Europe. A tangible manifestation of this was the biggest ever enlargement of the EU in 2004 and its next enlargement in 2007. Therefore the aim of this study is a formalized empirical evaluation of the phenomenon of integration in case of EU countries in the sphere of economic institutional order in the first decade of the twentieth century. Due to the fact that institutional systems should be treated as a multidimensional phenomena, in this study generally recognized taxonomic tools were used - a hierarchical classification method, which allowed to obtain some homogeneous subsets of countries classified on the base of institutional system similarities in each year. The study was based on annual data from the period 2000-2008 for 27 countries that are members of the EU. It allowed to capture a period of four years before and four years after the biggest enlargement of the EU. The main research problem of this study amounted to the question: whether in the analyzed period can one speak about the process of growing similarities in the sphere of institutional order in case of so called old and new EU member states? The study confirms existence of integration processes in relation to economic governance and institutional order.