The subject of this master's thesis is the judicial control of the legality of administrative action in the European Union. First, the introductory part of the paper shows the importance of administrative law for the functioning of the state and society, the main functions of administration and the importance of the legality of administrative actions. In addition, it clarifies how administrative law has become a significant and comprehensive part of EU law. Next, it explains the emergence of the European Union, its legal order and competences. Finally, the first chapter briefly analyzes the sources of EU administrative law in the frame of general sources of EU law. The main focus is put on regulations, directives and decisions, that make up secondary law of the European Union, i.e. general and individual administrative acts of the Union. The second chapter deals with the governing and executive bodies of the European Union whose actions, or failures to act, are supervised by the Court of Justice of the European Union. The subject of the third chapter is the principle of legality, as a fundamental principle of the legal system of each state, including the European Union, with a particular emphasis on the importance of legality in administrative action. The fourth chapter defines control of legality in administrative action in general, including the administration of the European Union, as a prerequisite for its legal action. Additionally, this chapter deals with administrative, judicial and other forms of control over administration, which is undoubtedly, the most important and effective judicial control, as the subject of this master's thesis. The last part deals with administrative disputes in the European Union for which is most important article 263, paragraph 4 of the Treaty on the Functioning of the European Union, because judicial control of the legality of administrative action in the European Union is exercised through administrative dispute.