Postumus Iunior (died 268) was an usurper against Roman Emperor Gallienus, according to the Historia Augusta. He is included in the list of the Thirty Tyrants.
According to the often unreliable list of Thirty Tyrants, the Emperor of the Gallic Empire Postumus had a son, also called Postumus, whom he nominated first caesar, and later even augustus and co-ruler. Postumus Iunior should have been killed together with his father, during the rebellion of Laelianus (called Lollianus by Historia).
The author(s) of Historia tells that Postumus Iunior was a skilled rhetor, and that his Controversiae were included among Quintilian Declamationes.