The Battle of San Marino was an engagement on 17–20 September 1944 during the Italian Campaign of the Second World War, in which German Army forces occupied the neutral Republic of San Marino, and were then attacked by Allied forces. It is also sometimes known as the Battle of Monte Pulito.

San Marino had declared its neutrality earlier in the war, and had remained broadly unaffected by events in Europe until 1943, when Allied forces had advanced a sizable distance up the Italian Peninsula. A major German defensive position, the Gothic Line, ran across the peninsula a short distance south of the Sammarinese border, and in late June, the country was bombed by the Royal Air Force, killing 35 people, in the belief that the German Army had taken up positions on its territory. In Operation Olive, launched in late August, a strong Allied force attacked at the very eastern end of the line, aiming to pass through Rimini—just east of San Marino—and break out onto the plains north of the city. Whilst San Marino was southwest of Rimini, the plan was for it to be bypassed entirely. In response to the Allied movements, the Germans sent a small force into San Marino to guard their lines of communication and act as artillery observers.

After a few days, the main thrust of the offensive was halted south of Rimini by strong resistance and severe weather, and the British and Indian flanking forces began to push westwards, taking the frontline towards San Marino. On 17 September the 4th Indian Infantry Division attacked forces of the 278. Infanterie-Division holding two hills just across the Sammarinese border; after heavy fighting to gain control of the hills, the situation stabilised on the 19th, and Allied forces began to push into the city of San Marino itself. The city was captured by the afternoon of 20 September, and the 4th Indian Division left the country on the 21st, leaving it under the control of the local defence forces.