This publication reviews and analyses the attitude of prominent spiritual leaders of Russian Orthodox Church toward the ideology and practice of Russian nationalism in the reign of the Emperor Nicholas II and in the period of the Civil war. On basis of different sources (verbatim records of the National Duma, periodical press publications, private sources, documents of the State Archive of the Russian Federation), this publication for the first time has a shot at giving an answer to the questions about the attitude of the Russian Orthodox Church in that period toward nationalism, at the reasons of cooperation of some prominent church leaders with political structures of Russian nationalists, as well as criticism of this political ideology on behalf of Orthodox clergy.