The Battle of Mons Lactarius took place in 553 during the wars of Justinian I against the Ostrogoths in Italy.

After the Battle of Busta Gallorum, in which the Ostrogoth king Totila was killed, the Byzantine general Narses captured Rome and besieged Cumae. Teia, the new Ostrogoth king, gathered the remnants of the Ostrogoth army and marched to relieve the siege, but in October of 553 Narses ambushed him at Mons Lactarius in Campania, near Mt. Vesuvius. The battle lasted two days, and Teia was killed in the fighting. The Ostrogoth power in Italy was eliminated, but Narses allowed the few survivors to return to their homes as subjects of the empire. The absence of any real authority in Italy immediately after the battle led to an invasion by the Franks, but they too were defeated and the peninsula was, for a short time, reintegrated into the empire.