The Battle of Mutina took place on 21 April 43 BC between the forces loyal to the Senate under Consuls Gaius Vibius Pansa and Aulus Hirtius, supported by the forces of Caesar Octavian, and the forces of Mark Antony which were besieging the troops of Decimus Brutus. The latter, one of Caesar's assassins, held the city of Mutina (present-day Modena) in Cisalpine Gaul.

The battle took place after the bloody and uncertain Battle of Forum Gallorum had ended with heavy losses on both sides and the mortal wounding of Consul Vibius Pansa. Six days after Forum Gallorum, the other Consul Aulus Hirtius and the young Caesar Octavian launched a direct attack on the camps of Mark Antony in order to break the front of encirclement around Mutina. The fighting was very fierce and bloody; the Republican troops broke into the enemy's camps but Antony's veterans counterattacked. Hirtius himself was killed in the melee while attacking Antony's camp, leaving the army and republic leaderless. Octavian saw action in the battle, recovered Hirtius' body, and managed to avoid defeat. Decimus Brutus also participated in the fighting with part of his forces locked up in the city. Command of the deceased consul Hirtius' legions devolved to Caesar Octavian. Decimus Brutus, marginalized after the battle, soon fled Italy in the hopes of joining fellow assassins Marcus Junius Brutus and Gaius Cassius Longinus. En route, however, Decimus Brutus was captured and executed, thus becoming the second of Caesar's assassins to be killed, after Lucius Pontius Aquila, who was killed during the battle.

After the battle, Mark Antony decided to give up the siege and skillfully retreated westward along the Via Aemilia, escaping the enemy forces and rejoining the reinforcements of his lieutenant Publius Ventidius Bassus. The battle of 21 April 43 BC brought the brief war of Mutina to a victorious end for the Republicans allied with Caesar Octavian, but the situation would change completely the following autumn with the formation of the Second Triumvirate of Antony, Octavian, and Lepidus.