Catherine of Austria (Portuguese: Catarina; 14 January 1507 – 12 February 1578) was Queen of Portugal as wife of King John III, and regent during the minority of her grandson, King Sebastian, from 1557 until 1562.

An Infanta of Castile and Archduchess of Austria, Catherine was the posthumous daughter of King Philip I and Queen Joanna of Castile.^[1] Catherine was born in Torquemada and named in honor of her maternal aunt, Catherine of Aragon. She was kept by her mentally-unstable mother's side.

All of her five older siblings, except Ferdinand, were born in the Habsburg Netherlands and had been put into the care of their aunt Margaret of Austria, but Joanna kept hold of young Catherine. Catherine actually stayed with her mother during imprisonment at Tordesillas during her grandfather Ferdinand II of Aragon's time as regent and her elder brother Charles as co-king. When the time came for her to marry, Catherine was released from the custody that her mother was to endure until her death.

On 10 February 1525, at the age of 18, Catherine married her first cousin, King John III of Portugal, she was married off to him by her mother Joanna I of Castile. They had nine children, but only two survived early childhood.

Catherine was very concerned about the education of her family, accumulating a substantial library and establishing a kind of salon in the court.^[2] She brought a number of women scholars into her household, including the humanists Joana Vaz and Públia Hortênsia de Castro, and the poet Luisa Sigea de Velasco.^[2][3] Vaz was responsible for tutoring Catherine's daughter, Princess Maria, as well as Catherine's niece, also called Maria, and a scholar in her own right.^[2][4]

After the death of her husband in 1557, she was challenged by her daughter-in-law and niece Joanna of Austria, over the role of regent for her grandchild, the infant King Sebastian. Mediation by Charles V resolved the issue in favor of his sister Catherine over his daughter Joan, who was needed in Spain in the absence of Philip II.

She then served as the regent of Portugal from 1557 until 1562. In 1562, she turned over the regency to Henry of Portugal.

Catherine had one of the earliest and finest Chinese porcelain collections in Europe due to her position as Queen of Portugal. "She acquired quantities of porcelain and exotica from Asia, which arrived regularly in Lisbon for the decoration of the Lisbon royal palace as well as for her personal use, and which served as emblems of her power. Her collection became the first kunstkammer on the Iberian Peninsula."^[5] She was following a tradition established earlier by the Portuguese King Manuel I of Portugal who had purchased porcelain for his wife, Maria of Castile (1482–1517), who was Catherine's aunt. Between 1511 and 1514, the Treasurer of the Spices in Lisbon "registered a total of 692 pieces of porcelain and other exotic goods" bought on his behalf for Maria of Castile, who was then King Manuel's second wife.^[6] Amongst other "exotica" in Catherine's collection were fossilized sharks' teeth, a snake's head encased in gold, heart-shaped jasper stones to stop bleeding, a coral branch used as a protector against evil spirits, bezoar stones, a unicorn's horn (a narwhal tusk) and piles of loose gems and stones such as rubies, emeralds, and diamonds.^[7]

Catherine has no descendants today, as both her grandchildren died childless. Her line of descent became extinct within six months of her death, as the only descendant of hers that survived her, King Sebastian of Portugal, died in August 1578.

Catherine of Austria figures in José Saramago's 2008 novel The Elephant's Journey. She also figures in Laurent Binet's 2019 novel Civilizations.

She was also featured in Kei Ohkubo's manga Arte, under the alias Irene at first; later, she revealed herself as Catalina, daughter to Juana of Castile. The timing was unspecified, but this fictitious arrival of Catalina at Florence could be some time between her release from custody and before her marriage; during her inner monologue, her brother, who had ordered a cardinal that was accommodating Catalina's trip to watch over her movements, was shown wearing a crown.