Flavia Julia Constantia (Greek: Κωνσταντία; after 293 – c. 330) was a Roman empress as the wife of Licinius. She was the daughter of the Roman emperor Constantius Chlorus and his wife Flavia Maximiana Theodora, and younger half-sister of Constantine the Great.

Constantia was one of six children born from the marriage of Constantius I and Theodora. Although her birth date has not been recorded, she must have been born after 293, as that was the year of her parents’ marriage.^[3] She had two sisters, Anastasia and Eutropia, and three brothers, Julius Constantius, Flavius Dalmatius and Hannibalianus.^[4] Constantius already had a son, Constantine I, from his previous relationship with Helena, making him Constantia’s half-brother.

In 313, the emperor Constantine gave her in marriage to his co-emperor Licinius, on occasion of their meeting in Mediolanum.^[5] She bore a son, Valerius Licinianus Licinius, in 315, and when the struggle between Constantine and Licinius began in 316, she stayed on her husband's side. A second war started between the two emperors in 324; after Licinius' defeat, Constantia interceded with Constantine for her husband's life. Constantine spared Licinius' life, and obliged him to live in Thessalonica as a private citizen, but the following year (325), he ordered that Licinius be killed. A second blow for Constantia was the death, also by order of Constantine, of her son Valerius.

In the following years, Constantia lived at her brother's court, receiving honors (her title was nobilissima femina). Constantia was her brother's favourite sister and proof of such favour is that he minted coins with her image and with the title "Constantia Soror Constantini AVG," or, "Constantia, Sister of Constantine Augustus" ("AVG" is an abbreviation of "Augustus," the center consonant being a "manuscript U," not a "V"). She converted to Christianity,^[6] supporting the Arian party at the First Council of Nicaea (325).^[7]

The city of Constanţa, Romania is named after her.