81st Regiment may refer to:
81st Regiment of Foot (Aberdeenshire Highland Regiment), a unit of the British Army, 1777–1783 81st Regiment of Foot (Loyal Lincoln Volunteers), a unit of the British Army 81st Infantry Regiment (PA), a unit of the Philippine Commonwealth Army during the Second World War 81st Infantry Regiment (Imperial Japanese Army), a unit of the Japanese Army 81st Assault Aviation Regiment, later Fighter-Bomber regiment, an aviation unit of the Yugoslav Air Force
American Civil War 81st Illinois Volunteer Infantry Regiment, a unit of the Union (Northern) Army 81st Indiana Infantry Regiment, a unit of the Union (Northern) Army 81st New York Volunteer Infantry, a unit of the Union (Northern) Army 81st Ohio Infantry, a unit of the Union (Northern) Army 81st Pennsylvania Infantry, a unit of the Union (Northern) Army
See also 81st Division (disambiguation) 81st Brigade (disambiguation) 81st Squadron (disambiguation)