- May 2, 1866 - In the Battle of Callao during the Chincha Islands War a Spanish Fleet took on an alliance of Peru, Bolivia, Chile and Ecuador.
- May 12, 1551 - King Charles I of Spain charts by decree the National University of San Marcos making it the oldest university in the Americas.
- May 15, 1544 - Blasco Núñez Vela entered Lima, the capital of the Viceroyalty of Peru, as the first of forty viceroys designated by the Spanish Crown.
- May 20, 1929 - The Peruvian Air Force was created by merging the aviation divisions of the Army and the Navy.
- May 26, 1880 - In the Battle of Tacna the alliance between Bolivia and Peru is broken by the Chilean General Manuel Baquedano near the city of Tacna..