May 12
- 1817 – The Congress of Tucumán starts its series of sessions in Buenos Aires.
- 1821 – The first edition of El Argos, Buenos Aires' first journal, on which some famous personalities wrote, including Ignacio Núñez, Manuel Moreno and Esteban de Luca.
- 1986 – Dies the socialist politician Alicia Moreau de Justo,who , with her jusband, Juan B. Justo was one of the most important people of socialism in Argentina.