Eustathius I

Eustathius I may refer to:


 * Eustathius of Antioch, Patriarch in 324–337 or 360
 * Patriarch Eustatius of Alexandria, Greek Patriarch of Alexandria in 813–817
 * Eustathius of Constantinople, Ecumenical Patriarch in 1019–1025
 * Jevstatije I, Serbian Archbishop in 1279–1286