The dogma of the Immaculate Conception, proclaimed by the Council of Basel on 17 September 1439, had theological and political significance. After the deposition of Pope Eugene IV, the council fathers prioritized this doctrine. The Dominican Juan de Torquemada opposed it on theological and ecclesiological grounds, arguing that an excommunicated council lacked the authority to establish dogmas. The preaching of Marcus Bonifili, Basel’s legate de latere in Kraków, had a clear political dimension. His Marian sermons, delivered in the 1440s in Kraków’s churches, including the Church of the Holy Trinity and the Church of the Blessed Virgin Mary, declared support for the council and served as a strategic tool. Bonifili intertwined theology and politics, using religious arguments to strengthen the council’s position. This presentation will analyze his sermons (1444–1447) and their manuscripts, exploring their audience and the extent of pro-conciliar sympathies in Kraków’s intellectual circles