81st Regiment

81st Regiment may refer to:


 * 81st Infantry Regiment (Philippine Commonwealth Army), a unit of the Philippine Commonwealth Army during the Second World War from 1942 to 1946.
 * 81st Regiment of Foot (Loyal Lincoln Volunteers), a unit of the United Kingdom Army
 * 81st Illinois Volunteer Infantry Regiment, a unit of the Union (Northern) Army during the American Civil War
 * 81st Assault Aviation Regiment, later Fighter-Bomber regiment, an aviation unit of the Yugoslav Air Force