The Battle of Long Tan (18 August 1966) took place in a rubber plantation near Long Tân, in Phước Tuy Province, South Vietnam, during the Vietnam War. The action was fought between Viet Cong (VC) and People's Army of Vietnam (PAVN) units and elements of the 1st Australian Task Force (1 ATF).

Australian signals intelligence (SIGINT) had tracked the VC 275th Regiment and D445 Battalion moving to a position just north of Long Tan. By 16 August, it was positioned near Long Tan outside the range of the artillery at Nui Dat. On the night of 16/17 August, mortars and recoilless rifles attacked Nui Dat from a position 2 kilometres (1.2 mi) to the east until counter-battery fire caused it to cease. The next morning D Company, 6th Battalion, Royal Australian Regiment (6 RAR), departed Nui Dat to locate the firing points and the direction of the enemy withdrawal. Weapon pits were found including mortars and RCLs. D Company clashed with VC around midday 18 August.

Facing a larger force, D Company called down artillery. Heavy fighting ensued as the VC attempted to encircle and destroy the Australians. After several hours two UH-1B Iroquois from No. 9 Squadron RAAF arrived overhead to resupply them. Supported by strong artillery fire, D Company held off a regimental assault before a relief force of M113 armoured personnel carriers and infantry from Nui Dat reinforced them at nighttime. The Australian forces had withdrawn to evacuate their casualties and formed a defensive position overnight. The next day Australian forces swept the area though the VC had withdrawn. The operation ended on 21 August.

Although 1 ATF initially thought it had suffered a defeat, it was later thought to have been a victory by preventing the VC from moving against Nui Dat. The battle's outcome was indecisive, with disagreements on its effect between the 275th Regiment and D445 Battalion. The D445 Battalion regarded the battle as a success, with the political victory of an effective ambush, and the securing of the areas around Long Tan village itself. Whether the battle impaired the capabilities of the VC is disputed.