51st Brigade or 51st Infantry Brigade may refer to:
Belarus 51st Guards Artillery Brigade
India 51st Indian Brigade of the British Indian Army in the First World War 51st Indian Infantry Brigade of the British Indian Army in the Second World War
Soviet Union 51st Guards Artillery Brigade
Ukraine 51st Guards Mechanized Brigade (Ukraine)
United Kingdom 51st (Ulster) Anti-Aircraft Brigade 51st Infantry Brigade (United Kingdom) Artillery units 51st (Lancashire and Cumberland) Brigade, Royal Field Artillery 51st (Westmorland and Cumberland) Brigade, Royal Field Artillery 51st (London) Anti-Aircraft Brigade, Royal Garrison Artillery 51st (Cornwall and Warwickshire) Medium Brigade, Royal Garrison Artillery 51st (Midland) Medium Brigade, Royal Garrison Artillery
See also 51st Army (disambiguation) 51st Division (disambiguation) 51st Regiment (disambiguation)