121st Brigade may refer to:
- 121st Brigade a 'bantam' infantry formation of the British Army 1915–18
- 121st Infantry Brigade a deception formation of the British Army in Sicily 1943–44
- CXXI Brigade Royal Artillery a British Army unit 1915–16
- 121st Artillery Brigade of the former Soviet Ground Forces
- 121st Brigade of the Chinese Republican army 1932
- 121st Field Artillery Brigade of the Egyptian Army
- 121st (Independent) Infantry Brigade of the Indian Army
- 121st Tank Brigade of the Red Army 1942
- 121st High-Power Howitzer Artillery Brigade of the Red Army 1945
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