| Peter de Lencastre | |
| marquis of Torres Novas | |
| Succession: | 5th Duke of Aveiro |
| Reign: | 1666–1673 |
| Predecessor: | Raimundo, 4th Duke of Aveiro |
| Successor: | Maria de Guadalupe, 6th Duchess of Aveiro |
| House: | House of Aviz |
| Father: | Álvaro, 3rd Duke of Aveiro |
| Mother: | Juliana de Lencastre |
| Birth Date: | 1608 |
| Birth Place: | Azeitão |
| Death Date: | 1673 |
| Death Place: | Lisbon |
Pedro de Lencastre, or Peter of Lencastre (Azeitão, 1608 – Lisbon, 1673), was the youngest son of Álvaro and Juliana of Lencastre, 3rd Dukes of Aveiro.
He studied theology in the University of Coimbra and he became successively Bishop of Guarda, Archbishop of Évora and Archbishop of Braga.
In spite of the Portuguese revolution against the Spanish Habsburgs, his nephew, Raimundo of Lencastre, 4th Duke of Aveiro actively supported the rights of the Habsburg Kings and, in 1663, the new King of the Braganza Dynasty, John IV, decided to confiscate the Dukedom.
However, Peter of Lencastre, a Braganza supporter, requested the cancellation of this decision and, finally in 1668, he was recognised as 5th Duke of Aveiro and Marquis of Torres Novas.
Later the same year, when the peace between Portugal and Spain was signed, Peter's niece, Maria de Guadalupe of Lencastre, sister and heir of the 4th Duke, requested the cancellation of the decision that granted the Dukedom of Aveiro to her uncle, in order to obtain it for herself.
Due to Peter of Lencastre's death in 1673, Maria de Guadalupe of Lencastre, still living in Spain, was recognised as the new Duchess of Aveiro on condition she would return to Portugal.