The proposed paper aims to analyze the vision of Joseph Cardijn, Belgian priest and founder of the Catholic Workers Youth (JOC), on the potential and development of social Catholicism in Chile and Argentina in the 1940s to 1960s. After World War II, Cardijn traveled several times to both countries and recorded his impressions about the need for social Catholicism and the fight against communism during the emerging Cold War. At the same time, his presence had a strong impact on the development of the JOC in both countries. Starting from Cardijn's own annotations, collected in the Cardijn archive in Brussels, which are contrasted with the local sources of the JOC in Chile and Argentina, the aim is to comparatively analyze the state of social Catholicism in Chile and Argentina, seen by a foreign, but very influential, observer. The hypothesis is that Cardijn's presence in Chile and Argentina had a great influence on the development of the JOC organization, since he provided a political frame of reference, the fight against communism, for the legitimization of the JOC, which was received in a somewhat different way by the ecclesiastical hierarchy in both countries. This different impact can help us better understand the development of social Catholicism and certain differences in the relationship between the hierarchy and progressive Catholics in both countries. Thus, new light can be shed on the fight against communism in Argentine and Chilean Catholic circles and, due to the transnational analysis, it is possible to highlight the differences and similarities between both countries. Furthermore, Cardijn's vision can be contrasted with the development of the JOC in both countries in order to reach a more balanced judgment on the importance of social Catholicism in Chile and Argentina in important decades for the history of the Catholic Church in these countries.