121st Regiment or 121st Infantry Regiment may refer to:
121st Regiment of Foot (disambiguation), several units 121st Regiment (Xinjiang Production and Construction Corps), People's Republic of China 121st Infantry Regiment (France) 121st Anti-aircraft Artillery Regiment "Ravenna", Italy 121st Infantry Regiment "Macerata", Italy 121st Infantry Regiment (United States) 121st Field Artillery Regiment (United States)
Union (Northern) Army in the American Civil War 121st New York Infantry Regiment 121st Ohio Infantry Regiment 121st Pennsylvania Infantry Regiment
See also 121st Battalion (disambiguation) 121st Brigade (disambiguation) 121st Division (disambiguation)