The article is on the history of the Department for the Spiritual Affairs of the Foreign Confessions within the Russian Empire Ministry of Interior Affairs in the early XXth century. The author examines the Russian State Historical Archive documentary sources which were not published before and identifies various duties of the Department officials. It's not only religious life control and legal regulation in Russia was among them. The regular reports and query answers from various regional administrative establishments were accumulated in the Department. They were used by the officials to collect and analyze the evidence on the current state of religions, not orthodox churches, religious organizations and minorities represented in Russia and also peculiarities of the Russian religious legislation and its administration. The results of this work where represented in the Department officials' investigations and publications. The existence of the Research Library founded in 1864, the Newspaper desk established in 1909 and the Archive was a principal condition that provided the high quality and profoundness of Department officials' investigations. The Research Library was regularly systemized and replenished with relevant publications. The access to the Department Archive was open for a wide range of researchers of the State-Church relationships in Russia. The all mentioned above facts allow for the conclusion that the Department for the Spiritual Affairs of the Foreign Confessions within the Ministry of Interior Affairs was one of the important but not well investigated establishments for religious study in the Russian Empire in the early XXth century.