81st Brigade may refer to:
Romania 81st Mechanized Brigade (Romania), a unit of the Romanian Army
Russia 81st Special Forces Brigade
Spain 81st Mixed Brigade, a unit of the Spanish Republican Army
Ukraine 81st Airmobile Brigade (Ukraine), a unit of the Ukrainian Air Assault Forces
United Kingdom 81st Brigade (United Kingdom), a formation of the British Army in the First World War 81st (Howitzer) Brigade, Royal Field Artillery, a unit of the British Army in the First World War 81st (Welsh) Brigade, Royal Field Artillery, a unit of the British Army after the First World War
United States 81st Stryker Brigade Combat Team
See also 81st Division (disambiguation) 81st Regiment (disambiguation) 81st Squadron (disambiguation)