The attitude to the notion of “the proving limits” in the criminal process science is controversial: starting from equation of it to “the subject of proving” and finishing with the attempts to identify it as a separate notion through such categories as limits, extent, depth, broadness, level, fullness, width, etc. Herewith the significant role in determination of the proving limits is highly desirable for the development of both the theory of process and the practical proving is recognised. The author analyses the existing theoretical views on the essential matter and proves limits and substantiates of the potential study of these views that would be based on principals of rational formalism. The author claims, that rational formalism as a method of the legal theory of proving does not contradict the contemporary concept of free judicial conviction. As the result of the study, the author offers his own notion of “proving limits” as a number of sources of prove which is required for judgment rational. Wherein the quantitative component of the notion “proving limits” can be expressed in the following ways: by the available sources provided by law; in a possible reference to specific source in the law (the obligatory proving limits); as one of the obligatory legally defined sourses.