Although there is no uniform definition of procedural principles in criminal procedure theory, they can be defined as legal rules or guidelines on which the criminal proceedings are based. As such, the principles of criminal procedure law apply to procedural entities and procedural actions. Evidentiary actions, as a type of procedural action, clarify the criminal case that is the subject of the criminal proceedings. The Criminal Procedure Code stipulates several evidentiary actions, one of which is the preliminary hearing of the defendant. The defendant hearing, in which the defendant gives their testimony, is given a great deal of attention because it represents one of the most important pieces of evidence, and the course of evidence presentation is the most significant and crucial issue of the criminal proceedings. Therefore, the paper will present a review of the criminal procedure principles related to this evidentiary action, starting from the principle of legality as the main principle, followed by the principles of orality, publicity, immediacy and adversity (party control of facts and means of proof).