It is indicated that the relationship between the Church and the state went through various stages in its formation both in Ukraine and in the world as a whole. In addition, the state’s relations with religious organizations in various countries still have their own specifics. Models of these relationships are usually built depending on the political, religious, cultural and other traditions of each region. Therefore, today in Europe, despite the presence of a number of common trends, there is still no unity of approaches in building a system of state-church relations. It is quite obvious that in order to solve this problem, it is necessary to study the existing historical experience of Czechoslovakia. Regarding this, the confessional policy of the Czechoslovak state in the 20th century has a special value. Back in the interwar twentieth century (1918–1938), an attempt was made here to build such a model of the relationship between the state and religious organizations, which, on the one hand, provided for the secular nature of the state and the maximum limitation of the role of the church in public life, and on the other hand, the preservation of the main elements of the system of state -church relations that developed in Austria-Hungary. We can say that in a slightly modified form this model continued to exist in Czechoslovakia and in the second half of the 20th century. Even during the years of state atheism, the church here was not separated from the state. Thus, in the 20th century, Czechoslovakia accumulated rich experience in adapting traditional elements of the state church to new historical conditions. Based on the study of domestic and foreign sources, the article analyzes the legal regulation of state-church relations in the First Czechoslovak Republic. The study attempted to analyze the country’s relationship with the Vatican, which consisted primarily of the need to conclude a concordat agreement. The legal nature of Modus vivendi is analyzed. It was determined that the model of state-church relations in the first Czechoslovak Republic became an organic development of the model that existed in Austria-Hungary. It can be said that the process of equalizing the rights of all state-recognized denominations came to a certain logical conclusion in the first Czechoslovak Republic. At the same time, one of the fundamental principles of Austrian religious policy was preserved in the Czechoslovak Republic – the desire to limit the ties of local denominations with foreign administrative centers as much as possible.