Castro Marim is a town and a municipality in the southern region of Algarve, in Portugal.

The municipal holiday is June 24.

In the Roman era, Castro Marim was known as Aesuris.

Every year in the end of August there is a Medieval Fair/Festival that reunites many people from across the world to perform, like medieval musicians, archers, swordsmen, dancers, troupes, etc. There are sellers too: blacksmiths, textile crafters (weaving), herbs sellers, etc.

In honour to his Portuguese mother, Lucia Gomes, from Castro Marim, Paco de Lucía - the Spanish composer and guitarist - named his thirteenth studio album Castro Marín.