Iulla Antonia or Julia Antonia, was a daughter of Roman consul Iullus Antonius and Claudia Marcella Major. Her elder brothers were Lucius Antonius and Gaius Antonius. Her maternal half-siblings were Vipsania Marcella and Appuleia Varilla.
Iulla’s maternal grandparents were Octavia Minor (second elder sister,and full sister to Roman Emperor Caesar Augustus) and her first husband, the Roman consul Gaius Claudius Marcellus Minor. Her paternal grandparents were Fulvia and the Roman Triumvir Mark Antony. Through her paternal grandmother, she was a descendant of the Roman politician Gaius Gracchus and the Roman General Scipio Africanus Major who defeated Hannibal.
Iulla was born in Rome, after 19 BC and was raised there. In 2 BC, her father was executed by her great-uncle, because he had an affair with Augustus’ daughter Julia the Elder.