Theodosius I (disambiguation)

Theodosius I (347–395) was Roman Emperor from 379 to 395.

Theodosius I may also refer to:


 * Pope Theodosius I of Alexandria (died 567), Patriarch of Alexandria, 535–567
 * Theodosius I of Constantinople, (died after 1183), Ecumenical Patriarch of Constantinople, 1179–1183
 * Teodósio I, Duke of Braganza (1510–1563), Portuguese duke