Theodosius (from the Greek "Θεοδόσιος", "Given by god") is a name which might refer to one of several people:
- One of three emperors of ancient Rome and Byzantium:
- Theodosius I (347–395; "Theodosius the Great"), son of Count Theodosius
- Theodosius II (408–450)
- Theodosius III (715–717)
- One of three popes of the Coptic Orthodox Church
- Pope Theodosius I of Alexandria
- Pope Theodosius II of Alexandria
- Pope Theodosius III of Alexandria
- One of three Patriarchs of Alexandria
- Patriarch Theodosius I of Alexandria (535–567)
- Patriarch Theodosius II of Alexandria (12th century)
- One of three Dukes of Braganza
- Teodósio I, Duke of Braganza (1510–1563), 5th Duke of Braganza
- Teodósio II, Duke of Braganza (1558–1630), 7th Duke of Braganza
- Teodósio, Prince of Brazil (1634–1653), 9th Duke of Braganza and 1st Prince of Brazil
Others by the name are:
- Theodosius of Bithynia or Theodosius of Tripolis (c. 160 BC – c. 100 BC) was a Greek astronomer and mathematician
- Theodosius Florentini, a Swiss Capuchin monk, a founder of Catholic religious orders
- Theodosius the Cenobiarch (c. 423–529)
- Theodosius, bishop of Philadelphia, deposed at Council of Seleucia, 359
- Theodosius (son of Maurice) (583/585–602), eldest son and co-emperor of the Byzantine emperor Maurice
- Theodosius the Deacon, a 10th-century Byzantine poet who wrote the poem "The Conquest of Crete"
- Theodosius of Kiev, 11th century Russian saint
- Theodosius, Metropolitan of Moscow (1461–1464)
- Metropolitan Theodosius (Lazor), former primate of the Orthodox Church in America (1933– )
- Theodosius Dobzhansky, noted geneticist and evolutionary biologist