The aim of this study is to compare how the Catholic Church’s involvement in politics under authoritarian rule in Spain and Poland impacted on religiosity in those countries after the transition to democracy. The Catholic Church was a key political actor during the Franco regime in Spain and communist rule in Poland. However, the nature of its political involvement in each case was quite different: while in Spain the Catholic Church legitimized the Franco regime, in Poland it was one of the main actors opposing communist rule. The authors use data from the Polish General Social Survey covering 1991–2008 and several surveys carried out by the Spanish Centre for Sociological Studies (CIS) between 1975 and 1995. Results confirm that the political involvement of the Catholic Church had different impacts on subsequent religious practice in each country. In Spain secularization was especially intense during the political transition in the late 1970s, while in Poland after the 1990s there was only a moderate shift toward secularization.