The gens Ninnia was a plebeian family at Rome. Members of this gens are first mentioned at Capua during the Second Punic War, and are found at Rome towards the end of the Republic.
The Ninnii appear to have been of Campanian origin. Two brothers of this family hosted Hannibal when he entered the city of Capua in 216 BC, in the aftermath of the Battle of Cannae. Livy identifies them as members of the noble Capuan house of the Ninnii Celeres.
The Ninnii Celeres used the Oscan praenomina Sthenius and Pacuvius. A branch of the family at Rome in the first century BC used the Latin praenomen Lucius.
Two cognomina of the gens are known from Republican times: Celer, which means "swift", belonged to a family of the Ninnii at Capua during the Second Punic War. The surname Quadratus is found amongst the Ninnii at Rome in the time of Cicero.