| Consort: | yes |
| Succession: | Queen consort of Portugal |
| Reign: | 1 December 1640 – 6 November 1656 |
| Succession1: | Queen Regent of Portugal |
| Birth Date: | 13 October 1613 |
| Birth Place: | Sanlúcar, Spain |
| Death Place: | Lisbon, Portugal |
| Burial Place: | Pantheon of the Braganzas |
| Spouse: | João IV of Portugal |
| House: | Medina Sidonia |
| Father: | Manuel, 8th Duke of Medina Sidonia |
| Mother: | Juana de Sandoval y la Cerda |
| Signature: | Assinatura D. Luísa de Gusmão.svg |
| Full Name: | Luisa María Francisca de Guzmán y Sandoval |
Luisa María Francisca de Guzmán y Sandoval (Portuguese: Luísa Maria Francisca de Gusmão;[1] 13 October 1613 – 27 February 1666) was Queen of Portugal as the spouse of King John IV, the first Braganza ruler. She was the mother of two kings of Portugal (Afonso VI and Peter II) and a queen of England (Catherine of Braganza). She served as regent of Portugal from 1656 until 1662.
Luisa was Spanish by birth, the daughter of Manuel Pérez de Guzmán y Silva, 8th Duke of Medina Sidonia, and Juana Gómez de Sandoval y de la Cerda. Her paternal grandfather was Alonso Pérez de Guzmán y Sotomayor, 7th Duke of Medina Sidonia, while her paternal great-grandmother was Ana de Mendoza y de Silva, Princess of Éboli. Through her mother, she was also a descendant of Isabel, Lady of Viseu, the illegitimate daughter of King Ferdinand I.
She married a high ranking Portuguese noble, John, 8th Duke of Braganza, in 1633, during the period of the Iberian Union.
Despite her Spanish roots, Luisa guided her husband's policies during the Portuguese revolution against Habsburg Spain of 1640. She is considered the main influence behind his acceptance of the Portuguese throne. It is said that being warned of the dangers of becoming queen of a country that was to face Spain's might, she pronounced the famous words:
Antes Rainha um dia que Duquesa toda a vida.Rather Queen for a day than Duchess all my life.
In some sources, this is quoted as for an hour instead of for a day.
When she was made aware of a failed attempt to murder the King in 1641, she is said to have been one of the members of the Corte, which supported the execution of nobles like the Duke of Caminha.
In 1656, she was named Regent of the Kingdom after her husband's death and during the minority of her son Afonso VI.
Luisa was politically astute and mainly responsible for the diplomatic success of the new alliance with England. Her daughter Catherine married Charles II of England.
Afonso was considered mentally unfit for governing. In addition to lacking intellect, he exhibited wild and disruptive behavior. In 1662, after the king terrorized Lisbon at night alongside his favorites, Luisa and her council responded by banishing some of the king's companions that were associated with the raids. Angered, Afonso took power with the help of Castelo-Melhor and Luisa's regency came to an end. She subsequently retired to a convent,[1] where she died in 1666.