Dionysius I
# Dionysius I

Dionysius I may refer to:

* Dionysius I of Syracuse (ca. 432–367 BC), Greek tyrant of Syracuse
* Dionysius I (Syriac Patriarch), or Dionysius Telmaharensis (died 845), Patriarch of the Syriac Orthodox Church
* Dionysius I, Metropolitan of Moscow (died 1385)
* Patriarch Dionysius I of Constantinople (died 1492), Patriarch of Constantinople
* Mar Dionysius I (died 1808), Metropolitan of the Malankara Church
