The article examines the role of the last Jagiellonian monarchs, Sigismund I (1506-1548) and his son Sigismund II Augustus (1548-1572), in promoting and securing religious peace in the multi-confessional society of the 16th-century Rzeczpospolita. The author argues that the Jagiellonian dynasty, which ascended to the Polish throne in 1386 and ruled until 1572, contributed significantly to the rise of religious pluralism in Poland and Lithuania, and paved the way for a mechanism of tolerance which made it possible for religious groups to live together and to respect their religious diversity. The author analyses the anti-heretical laws passed by Sigismund I in the 1520s, and Sigismund II in the 1550s, which were intended to suppress the dissemination of Reformation ideas. In these documents, both monarchs declared their loyalty to the Roman Church, and threatened followers of the Reformation with severe penalties. All these documents give an insight into the religious policy of the Polish kings. Anti-heretical legislation was just one part of a more complex and sophisticated policy of the Jagiellonian kings, which aimed at preserving the religious status quo in the multi-ethnic and multi-confessional Rzeczpospolita.