The purpose of the research is to analyze relіgіous life of the Roman Catholics in UkrSSR during the period from the Second Half of 1940 - First Half of 1980s. The main object of the study is average believers and manifestations of their religiosity. The research methodology. Among the methodological approaches (as research directions) were used concrete - historical and cultural-anthropological ones. For realization of scientific tasks the following methods were employed: analysis and synthesis, historical-genetic, historical-problem, historical-comparative, historical-typological. The scientific novelty. The article elucidates little-known aspects of the history of the Roman Catholics' religious life in Soviet Ukraine, changes in the network of their communities, and the quantitative composition of believers and clergy, which were mainly caused by Soviet anti-religious policy. The religious manifestations of the Roman Catholics, their ritual activity, including believers' attendance of worships are traced. Conclusions. The religious policy of the Soviet authorities regarding Roman Catholics in the post-war period was ambiguous. Although the Roman Catholic Church was allowed to exist legally, it was perceived as being governed by a center hostile to USSR. Therefore, considerable efforts were made to weaken its structures. In the last third of the 1950s, an active attack on various denominations by the state began. Roman Catholics also became the object of pressure. The churches were closed, the pressure was exerted on the believers. In the mid-1960s, the government abandoned direct violations of constitutional norms in the religious sphere. The fight against religion became more hidden. Emphasis was placed on antireligious propaganda and the spread of atheistic outlook. Throughout the period under the study, Roman Catholics displayed relatively high levels of religiosity, religious consciousness and behaviour. They had a higher proportion of worshipers than the Orthodox. Some of their communities, even when they were unregistered, continued to operate illegally. However, the total number of Roman Catholics, especially the deeply believing believers, was steadily decreasing. Believers more rarely turned to God, relied on him, religious ideas were losing their influence and were shifting to the periphery of religious consciousness. The total number of people who regularly attended temples, participated in worships, confessed, took communion, performed life cycle rituals and other religious activities etc. significantly decreased. In general, it can be stated that the religious behavior of Roman Catholics has been strongly influenced by secularization processes. [ABSTRACT FROM AUTHOR]