Marquis of Porto Seguro (in Portuguese Marquês de Porto Seguro) was a Portuguese title of nobility created by a royal decree of king Philip III of Portugal (aka Philipe IV of Spain) dated from 8 April 1627, and granted to D. Afonso of Lencastre, 2nd son of Álvaro of Lencastre, 3rd Duke of Aveiro. Afonso always supported the Habsburg kings and even after the Portuguese revolution of 1 December 1640, he remained faithful to the Spanish Dynasty.