The purpose of this study is to present the religious life of the Old Believers in the Ekaterinoslav diocese of at the beginning of the 20th century and analyze the specific nature of the Orthodox mission activities in their midst. The research methodology is based on the principles of historicism, consistency, author’s objectivity, as well as on general scientific (analysis, synthesis, concretization, generalization) and special historical (problem-chronological, historical-genetic, historical-typological) methods. The problem-chronological method has been employed to analyze the religious life of the Old Belief communities in the Ekaterinoslav diocese and reveal the religious policy of the official Orthodox Church towards the Old Believers in the specified period. The historical-genetic method has been applied to analyze the transformations of the Old Belief in the Ekaterinoslav diocese and examine the confessional policy of the Orthodox Church. The historical-typological method has been adopted to study the internal separation and conflicts in the Old Belief of the Ekaterinoslav diocese and consider the forms of religious policy implementation. The scientific novelty of the undertaken researchlies in the fact that for the first time the internal distribution of the Old Belief in the Ekaterinoslav diocese has been comprehensively studied, the course of the conflict between the okruzhniki and the neokruzhniki has been disclosed, the forms and methods of missionary activity of the official Orthodox Church have been presented. Conclusions. At the beginning of the 20th century, 10 000 Old Believers lived in the Ekaterinoslav diocese. The popovtsy represented the overwhelming majority; the neokruzhniki, the bespopovtsy, and the beglopopovtsy were made up groups. The relations with priests, whose actions provoked indignation among the parish, caused the internal conflicts in the communities. The case of the priest S. Tokarev gained special publicity. The conflict was acute in popovshchina, between the okruzhniki and the neokruzhniki, that gradually began to decline after the act of reconciliation in 1906. On the way to reconciliation, the community of the okruzhniki faced an alleged provocation against Archbishop Ioann. The «fight» against the Old Believers remained the priority in the activities of the Orthodox missionary. The diocesan missionaries were opposed both by the representatives of the clergy and the ordinary Old Believers, and the authorities, namely the Old Belief nachyotchiki K. Peretrukhin, V. Zelenkov, L. Pichugin, and others. Despite the high level of organization and activities of the missionary institute, the immediate success of the mission was limited.