The article focuses on the issues pertaining to the boundaries of competence enjoyed by prosecutor and investigator when preparing the bill of indictment, since these issues are of vital importance for the modern law administration practice. The author emphasizes that the topic concerned partly ensues from the uncertainty of current criminal procedural legislation since it does not allow coming to an explicit conclusion about the time of making the bill of indictment and about the subject who should make it; this situation also partly stems from unavailability of sustainable approaches in the criminal process science which could clarify the correlation of powers enjoyed by prosecutor – procedural supervisor and investigator. The purpose of the article is to draw attention to the problems arising between prosecutor-procedural supervisor and investigator conducting pre-trial investigation at the stage of its completion, and to analyze these problems through the prism of a systematic interpretation of provisions consolidated in current criminal procedural legislation, and also to formulate practical recommendations aimed at resolving the existing problems. The lack of legal certainty in legislation entailed the situation when in the law administration practice it is not infrequent that investigators refuse to make the bill of indictment after opening of the materials of criminal proceedings, in cases where they do not agree with the position of prosecutor – procedural supervisor and where they insist that prosecutor is entitled to make the bill of indictment him-/herself and pursue the charge in court. The author emphasizes that investigator and prosecutor are actually the prosecution and should join and direct their efforts with a view to achieving the goals of criminal proceedings; there should be no confrontation between them, since it negatively affects the authority of the bodies which should strictly comply with requirements of current criminal procedural legislation, and should jointly combat crime and contribute to the achievement of the goals of criminal proceedings. The article notes that scientific approaches to investigator - prosecutor relations which were developed in Soviet times and were regarded by national scholars as sustainable, can no longer be used, since the idea of the function which the prosecution has in the criminal process and the idea of current criminal procedural legislation in general has been conceptually changed. By nature and orientation, investigator’s functions in criminal proceedings remain multifold, and this is the reason giving rise to diametrically opposed approaches to the understanding of investigator’s functional focus. Without going deep into the problematics of investigator’s functional orientation in criminal proceedings, the author centers on the relations which arise between prosecutor – procedural supervisor and investigator carrying out pre-trial investigation at the stage of completion of pre-trial investigation, and on the challenges arising in practice. Based on the findings of the author’s research and interpretation of some provisions of current criminal procedural legislation regarding investigator – prosecutor relations at the stage of completion of pre-trial investigation, the article draws certain conclusions: the science of criminal procedure lacks comprehensive research aimed at developing the doctrinal ideas of the functional orientation of investigator’s criminal procedural function and its correlation with the function of prosecutor; having recognized the evidence collected during pre-trial investigation as sufficient for the bill of indictment, prosecutor or investigator on prosecutor’s behalf is under the obligation to inform the suspect or his/her counsel about completion of pre-trial investigation and to open the access to the pre-trial investigation materials; after the materials are opened and made available to the other party, investigator is under the obligation to make the bill of indictment; making of the bill of indictment by prosecutor is prosecutor’s discretion and may be exercised, for example, if prosecutor disagrees with the bill of indictment made by investigator; prosecutor is authorized to instruct investigator to carry out investigative (detective) operations, covert investigative (detective) operations, or other proceedings within the period established by him/her, or to give instructions regarding such measures or take part therein, and, if necessary, to personally carry out investigative (detective) operations and other proceedings in the manner prescribed by the Code of Criminal Procedure of Ukraine; criminal procedural legislation does not grant prosecutor the right to give instructions to investigator with regard to making of a procedural decision, including the bill of indictment.