The article examines the principles of law as interpreted by Russian liberal jurists of the late XIX – early XX centuries – N.K. Rennenkampf, G.F. Shershenevich, S.V. Pakhman and M.N. Kapustin. In the absence of special studies that allow to study the principles of law in the legal science of the Russian Empire the author reveals the signs identified by domestic scientists in understanding the guiding principles of legal regulation; the characteristic of the principles of legality, justice, humanism, democracy and formal equality proposed by lawyers of the pre-revolutionary period at the stage of problem formulation is presented. Special attention is paid to the concept of M.N. Kapustin according to which the legal sphere focuses on two types of principles at once: some carry the basic meaning of law and are an integral part of its essence (justice and formal equality), others are introduced artificially in the course of human mental activity in order to optimize the processes of creation, application and development of legislation. It is proved that the Russian jurists of the late XIX – early XX century insist on the scientific development of the principles of law and their investment in the form of legal norms that have a constituent character, direct action, stability and formal certainty. It is noted that the supporters of legal positivism, emphasizing the importance of legal doctrine and firmly fixing the term ≪principle≫ in scientific circulation, had a significant impact on the formation of the modern categorical apparatus. The relevance of the views of liberal jurists of the late XIX – early XX century, projecting the effect of the principles of law on overcoming gaps in legislation and optimizing law enforcement activities in terms of the exercise of discretionary powers is emphasized.