Theresa of Portugal (1176 – 18 June 1250) was Queen of Léon as the first wife of her first cousin King Alfonso IX of León.

[5] However, when her marriage to Alfonso was declared invalid because they were first cousins, she returned to the Kingdom of Portugal and lived in the Monastery of Lorvão, formerly under the Benedictine rule, which she converted into a Cistercian convent, with over 300 nuns.

Theresa negotiated the Treaty of Benavente by which Sancha and Dulce stepped aside and allowed Ferdinand III of Castile, Berengaria's eldest son, to take the throne of León.

After the succession dispute, Theresa returned to Lorvão and finally took her convent vows after years of living as a nun.

On 13 December 1705 Theresa was beatified by Pope Clement XI's papal bull Sollicitudo Pastoralis Offici, along with her sister Sancha.