Abstract: The research subject is the legal regime of initiation of a criminal case on the base of the materials of operational investigations. The paper analyzes the provisions of the existing criminal legislation and the legislation regulating operational investigations of law enforcement agencies. The research object is the range of social relations appearing on the stage of initiation of a criminal case when analyzing the reason for initiating a preliminary investigation on the base of the data acquired in the result of operational investigations. Special attention is paid to the concept of such a reason for initiation of a criminal case as a report of an official about the elements of crime. The author applies the set of general scientific and special methods of cognition including the normative-logical method, the system method, analysis, synthesis, deduction, induction and other research methods. The novelty of the study consists in the proposals about the development of forms and methods of legal regulation of the mechanism of initiation of a criminal case on the base of the materials of operational investigations. The author concludes that the procedural peculiarities of initiation of a criminal case on the base of operational investigation results are connected with collecting various operational documents (reports, certificates, acts, copies of official documents, and other materials reflecting criminal activity of the persons under investigation) using scientific and technological instruments. The persons involved in these documents collecting can be later interrogated as the witnesses in a criminal case. It will increase the validity of the collected evidential base and guarantee the operational information transformation into evidences and their use in criminal proceedings. The author declares the necessity to develop legal regulation of use of the materials, collected during investigational operations, in criminal proceedings.