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

• Theodosius (disambiguation), a given name, including a list of people with that name

This disambiguation page lists articles about people with the same name.
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