Euthymius or Euthymios (Greek: Εὐθύμιος) may refer to:
- Saint Euthymius the Great (377–473), Christian saint
- Saint Euthymius the Younger (823/4–898), Christian saint who lived at Mount Athos
Christian Patriarchs:
- Patriarch Euthymius I of Constantinople (834–917)
- Patriarch Euthymius II of Constantinople (c. 1340–1416)
- Patriarch Evtimiy of Bulgaria (Euthymius of Tarnovo) (1325–1402)
- Euthymius II Karmah, 17th-century Melkite Patriarch of Antioch
- Euthymius III of Chios, 17th-century Melkite Patriarch of Antioch
Other people:
- Euthymius of Sardis, Bishop of Sardis (840)
- Euthymius of Athos (ca. 955–1028), Georgian philosopher and scholar
- Euthymius of Constantinople (11th century), 11th-century monk
- Euthymius Zigabenus, 12th century monk and commentator of the Bible
- Euthymios Saifi (1643–1723), Melkite Catholic bishop of Tyre and Sidon
- Euthymios (Agritellis) of Zela (1876–1921), Greek Orthodox Bishop of Zela, in Amasia, Western Pontus
- Euthymius (Moiseyev) (born 1972), Russian Orthodox Bishop of Lukhovitsy