Infanta Isabel Luísa of Portugal (Lisbon, 6 January 1669 – Palhavã, 21 October 1690) was a Portuguese infanta (princess) and the sole daughter of King Peter II of Portugal and his first wife and former sister-in-law Maria Francisca of Savoy. As such she was styled Princess of Beira. She was the presumptive heir to the throne of Portugal between 1668 and 1689, the year her half-brother John was born.

Dona Isabel Luísa was the only child of Peter II of Portugal and his first wife the French born Princes Marie Françoise of Savoy. She was born at the Ribeira Palace in 1669.

She was planned to marry Victor Amadeus II of Savoy who was her first cousin by her aunt Marie Jeanne of Savoy, Duchess of Savoy and regent for her son. The marriage was opposed by most of the Savoyard court as it meant that Victor Amadeus would have to live in Portugal and his mother would remain in power (mother and son did not have a close relationship). As such the match was dropped.

Other proposed candidates included Gian Gastone de' Medici (future Grand Duke of Tuscany), le Grand Dauphin son of Louis XIV, Charles II of Spain, the Duke of Parma as well as a Count Palatine of Neuburg. Nothing came of these plans. For this she was nicknamed Sempre-noiva, "Always-engaged".

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