This article researches a system of sources of law during the UPR period, shows its content, role and meaning in process of establishing law and order in a state. We conducted, that a system of sources of law during the UPR period consisted of regulations and legal customs; legal consciousness also had a regulatory function. We concluded that the main source of law was regulations. It was proved, that there was only one body of legislative power that could adopt bills — Tsentralna Rada, and statutory instruments could be issued by executive bodies and local power. It is explored that only those regulations of former Russian Empire and Provisional Government were in effect on the territory of UPR, which were not canceled by Tsentralna Rada and were not contradicting the applicable legislation. It has been shown that those legal customs were in effect in UPR which demonstrated public law consciousness in lawmaking field and were reflected in land, family and hereditary legislation. We conducted, that sources of law in the field of law enforcement were professional legal consciousness of judge’s and public legal consciousness, where the latter was used during public proceedings, which was designed to implementation of regulations of common law.