Petronila of Aragon (Spanish: Patronilla Ramírez; French: Pétronille; also sometimes Petronella) (1135 – October 17, 1174, Barcelona) was Queen of Aragon from 1137 until 1162. She was the daughter of Ramiro II, King of Aragon, and Agnes of Aquitaine.

Petronila came to the throne through special circumstances. Her father, Ramiro, was bishop of Barbastro-Roda when his brother, Alfonso I, died heirless in 1134. As king, Ramiro received a papal dispensation to abdicate from his monastic vows in order to secure the succession to the throne. King Ramiro the Monk, as he is known, married Agnes, daughter of Duke Wiliam IX of Aquitaine and Gascony, and through her produced an heiress, Petronila. At two years old, Petronila was bethrothed to Ramon Berenguer IV, Count of Barcelona and, immediately thereafter, Ramiro abdicated in favour of his daughter and returned to monastic life.

The Aragonese monarchy had previously passed only to males, thus Petronila's succession was an exception at the time. Bastardy was not an impediment of succession in Aragon, the ancestor of this line, Ramiro I having been a bastard. The heir in male line, Garcia VI of Navarre, was genealogically relatively distant, son of Ramiro II's second cousin. Petronila's succession created a new case in succession custom in Aragon.

Petronila married Ramon Berenguer in 1150. While he was alive, they nominally ruled their possessions separately, although the count had the final say over both Aragon and Catalonia. Upon his death, Petronila renounced the crown of Aragon in favour of her eldest son, Ramon, who, in compliment to the Aragonese, changed his name to Alfonso. Her son was the first ruler of both Aragon and Catalonia (where he is known as Alfonso I) thereby establishing the dynastic union between the two countries that lasted until the Crown of Aragon was dissolved in 1707.