Problem setting. The article is devoted to detection of the legal nature of the relationships between EU Member States’ domestic law and newly-created system of patent law governance, which comprises the Council Regulations 1257/2012 on implementing enhanced cooperation in the area of the creation of unitary patent protection and № 1260/2012 on implementing enhanced cooperation in the area of the creation of unitary patent protection with regard to the applicable translation arrangements as well as the Agreement on a Unified Patent Court. The subject of this research are the potential challenges the enforcement of the EU law may pose to the Unified Patent Court, along with enforcing Contracting State’s domestic law and international treaties, binding to the Contracting States as well as potential threats that can emerge after the Unified Patent Court becomes operational, especially the threat of legal fragmentation in terms of patent relationships. Profound analysis of the rules, that set the procedure of using different types of legislation while hearing the patent disputes cases has been made. The legal opinions of the Court of Justice of the European Union concerning the autonomous judicial bodies and their influence on the EU law have been presented. Potential threats to the EU legal system’s integrity and possible ways of deterring them have been outlined. Comparisons between recent and previous legal problems concerning the field of the EU law integrity have been made. The main arguments of the Court of Justice of the European Union have been studied and the most durable ones have been stressed as the milestones of the future Unified Patent Court legal practice. Conclusions about the importance of domestic and EU law correlation in light of patent legal sphere have been made. The drawbacks of current EU legislation and the need for the Court of Justice of the European Union to reconsider its positions have been mentioned. Analysis of recent researches and publications. The problems of compiling EU rights and national rights of EU member states in the context of their use by EU institutions, as well as other bodies, in particular the ECHR, as well as the question of fragmentation of patent law, were raised by the following EU researchers: Kristof Krenn, Giuseppe Martinico, Jorg Polakiewicz, Sionaidh Douglas-Scott, Steve Peers, Douwe de Lange, Tatiana Komarova. Purpose of the research is to conduct a profound analysis of the problem concerning the use of EU law and other legal sources by the Unified Patent Court during its future legal practice and to study the bonds between the Court of Justice of the European Union, the Unified Patent Court and Contracting Member States and their role in the creation of the new legal framework. Article’s main body. The analytics of the EU patent law harmonization has been an object of attention of many researchers so far. For instance, Reto M. Hilty and the collective of authors, who studied the problem of enforcement of law, that forms the so-called «patent package», explicitly paid their attention to the question of jurisprudence fragmentation, the point of which is that as soon as the Agreement on a Unified Patent Court comes into force, several judicial bodies will cover the territory of the Contracting Member States with their jurisdiction simultaneously. Apart from the national courts, that will deal with the patents, issued by the domestic authorities, the following bodies will execute their functions: the Unified Patent Court on cases concerning the European patent with unitary effect, the Court of Justice of the European Union by issuing its preliminary opinions on the compatibility of the Unified Patent Court’s actions with the EU law and the Boards of Appeal of the European Patent Office by deciding on the administrative lawsuits. The problem of jurisprudence fragmentation entails a vast amount of problems, the answer to which can only be given by means of judicial practice. If we turn our view towards Article 7 of the Council Regulation № 1257/2012, we will notice that this article gives the European patent with unitary effect the meaning of property, that should be equally recognized throughout all the Contracting Member States. This aspect leads to an important conclusion, that will be discussed later in this paper. Conclusions and prospects for the development. To sum this up, it’s worth noting, that the beginning of the Unified Patent Court’s functioning, as well as the moment when the legislation, created by means of enhanced cooperation mechanism, comes into force, will certainly become a remarkable event both to the EU institutions and the Unified Patent Court, since it has the potential to become a strong incentive to reconsideration of current approaches to the cooperation between the EU and international judicial bodies.