The subject of the final paper is the principles of administrative procedure. The paper defines the administrative procedure and the administrative matter. The principles of administrative procedure are defined and explained in detail in the administrative procedure of the Republic of Croatia as well as in the administrative procedure of the EU law. This paper analyses the principles of administrative procedure within the framework of European Union law and in accordance with the Proposal for a Regulation of the European Parliament and of the Council on administrative procedures of the institutions, bodies, offices and agencies of the European Union and compares those with the principles of administrative procedure in General Administrative Procedure Act. In the Republic of Croatia there are 10 strictly defined principles, while in the European Union there are less principles which are not as strictly defined as in the administrative procedure of the Republic of Croatia. The paper presents examples of provisions of the General Administrative Procedure Act, which implement the principles of administrative procedure, and also monitors the regulation of these principles in the Administrative Dispute Resolution Act.