Leo III, Leon III, or Levon III may refer to:
- Leo III the Isaurian (685-741), Byzantine emperor 717-741
- Pope Leo III (d. 816), Pope 795-816
- Leon III of Abkhazia, King of Abkhazia 960–969
- Leo II, King of Armenia (c. 1236–1289), sometimes referred to as Leo III, ruled from 1269 to 1289.
- Leo III, King of Armenia (1287-1307), ruled from 1303 to 1307
- Other uses