Introduction. The Kazakh SSR used to be a most multiethnic and multiconfessional Soviet republic. The article deals with the understudied issue of religious communities and their development throughout the 1940s to early 1990s in Kazakhstan. Goals. The work examines archival sources for comprehensive insights into the history of the Republic’s Christian (with the exception of ROC-affiliated ones) sectarian communities, and seeks to outline some regional features of the latter. Materials and methods. The study focuses on record-keeping and statistical records contained in archival collections of regional, republican and all-Union plenipotentiaries representing corresponding Councils for the Affairs of Religious Cults (under Councils of People’s Commissars), letters of sectarians submitted to supreme government agencies. With due account of ideological essentials of the involved sources, methodological preference is given to critical and comparative analysis tools. Results. Special attention has been paid to little-known records housed at regional archives of Kazakhstan that reveal some local features of the religious groups, such as their large number that resulted from ethnic deportations (Germans, Poles, Latvians, Ukrainians) to the Republic, high levels of congregational diversity. The tough and controversial relations between the Government and those communities were rooted in strict control and discrimination of believers practiced by Soviet and party organs, imposed activity restrictions, prohibitions on public ritual performances, ‘excesses’ of local officials. Some groups (Catholics, Lutherans, Evangelical Baptists) were eager to get registered and would seek to compromise with authorities, while others (Subbotniks, Dissident Baptists, True Orthodox Christians) expressed open dissent against the Soviet religion-related laws and tended to avoid any such registration. The examined period witnessed virtually no changes in activity patterns even in the aftermath of the 1970s–1980s religious easements.