Portal:Catholic Church/Selected anniversaries/May 20
- 325 - The First Council of Nicaea – the first Ecumenical Council of the Christian Church – is held.
- 1277 - Death of Pope John XXI.
- 1444 - Saint Bernardino of Siena.
- 1690 - England passes the Act of Grace, forgiving followers of Roman Catholic James II.
- 1825 - Death of Papaflessas.
- 1906 - Birth of Giuseppe Siri.
- 1927 - Death of Franciszek Macharski.