Introduction. The article analyzes the transformation of the diocesan administration system of the Russian Orthodox Church (ROC) in one of the key periods of its recent history – from 1988 to 2008. The study focuses on the dioceses in the European part of Russia, which allows identifying regional specifics and general trends in the administrative-territorial reform of the church body after gaining religious freedom. The aim of the study is to analyze the prerequisites, content, and results of the development of the ROC diocesan administration system during the specified chronological period within the given region. Materials and methods. The work is based on the analysis of the texts of the ROC Statutes of 1988 and 2000, statistical data, materials of Local and Bishops' Councils, as well as scientific research on church history. The methodological basis consists of historical-systemic, comparative-historical, and diachronic methods, allowing to consider the transformation process in dynamics and in relation to the socio-political context of the era. Results and discussion. The study showed that the development of the diocesan network was determined by a complex of interrelated factors. The key ones were: the canonical principle of correspondence between church and civil administrative boundaries; the need for effective management in the conditions of the "church renaissance" and the rapid growth in the number of parishes and believers; the policy of regional authorities who saw the creation of a diocese as an element of prestige and sovereignty; the missionary task of countering the proselytism of other confessions. The work traces the gradual evolution from the initial enlarged division (1988) to active fragmentation in the 1990s and subsequent stabilization and unification of boundaries in the 2000s. Special attention is paid to the reform in national republics and large metropolitanates (using Moscow as an example). Conclusion. It is concluded that by 2008, a stable and optimized diocesan structure corresponding to the constituent entities of the Federation had been basically formed in the European part of Russia. The process of 1988–2008 laid the foundation for the modern administrative structure of the ROC, defining its basic principles: conciliarity in management, canonical correspondence to state borders, and adaptation to new social realities while preserving traditional church identity.