 From 1925 he was Professor of History of Christianity at the University of Rome; however, after the Concordat in 1929, the University forbade him to teach and to examine students, and he was given non-academic tasks, such as library investigation and the writing of research papers.In 1931 his university chair was definitively revoked, because he refused to swear the "oath of loyalty" to Fascism (all teachers were forced by law to swear an oath of loyalty to the Fascist government, and those who refused were fired).In his autobiography "Il pellegrino di Roma" ("The Pilgrim from Rome", 1945), Buonaiuti reconstructed the history of his conflict with the Catholic Church, of which he continued to claim himself a "loyal son", even after his excommunication.