Regius may refer to:
- Regius Professor, "Royal" Professorships at the universities of Oxford, Cambridge, St Andrews, Glasgow, Aberdeen, Edinburgh and Dublin
- Raphael Regius (c.1440–1520), Venetian humanist
- Henricus Regius (1598–1679), Dutch philosopher and physician
- Codex Regius, Icelandic manuscript in which the Poetic Edda is preserved
- Hippo Regius, ancient name of the modern city of Annaba, Algeria
- Titulus Regius, 1483 statute of the Parliament of England, giving the title "King of England" to Richard III
- Animal names:
- Python regius, python
- Argyrosomus regius, Meagre, Shade-fish, Salmon-Basse or Stone Bass
- Phidippus regius, Regal Jumping Spider
- Philautus regius, frog of Sri Lanka
- Hylodes regius, frog of Brazil
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