The study of the church historiography of the Ukrainian diaspora in the situation of the exacerbation of interchurch relations associated with the Ukrainian geopolitical factor is highly relevant. The works and views of diaspora historians were of great importance for the formation of the worldview of scholars in the Ukraine after the ideological barrier fell and the independent state was constituted. This research focuses on the publications of representatives of the Ukrainian diaspora in academic journals in honor of the millennium of Christianization of “Rus’-Ukraine”. The purpose of this article is a comparative analysis of publications of the diaspora historians and representatives of academic centers in Europe and America in the second half of the 1980s on the issues of Russian church history, a study of the nature of the relationship between professional and non-professional literature, the peculiarities of the methodology of church historical research of the diaspora scholars, their role in the development of the Ukrainian church historiography and knowledge of the history of the Russian Orthodox Church in South-Western Russia. No such study has been conducted so far. The author argues that the environment in which certain ideas were born and published had a great impact on approaches and understanding of the past in the works of the Ukrainian diaspora historians. Many of them are written under strong ideological influence, they expresses a very emotional attitude to the research subject and mixes the scientific approach with fiction. While real historical research was characterized by the full rejection of nationalist ideology and strict adherence to logic, the authors who blindly endorsed the nationalistic ideology adhered to “recognized” authorities, undetached attitudes, and emotional perception of church history. The studies with strictly scientific discourse avoid one-sided opinions, pay great attention to the analysis of historical sources and seek to interpret the facts of the past in the broad context of the world historical process.