MIO may refer to:
- Mio, Michigan, a town in the USA.
- mio, a written abbreviation for “millions” as a unit indicator in the financial markets.
- MIO, micaceous iron oxide, a type of hematite used in anti-corrosion paints, e.g., the top layer of paint of Eiffel Tower.
- Mio, an abbreviation for Mebioctet, a unit of information or computer storage.
- MIO (Department), MIO is short for Management Information Office, a department within Residence Life at the University of Wisconsin-Oshkosh.
- Masivo Integrado de Occidente, a bus-based mass-transportation system being constructed in Cali, Colombia.
- mio TV, a pay-TV service by SingTel.
- Mio Technology, a Taiwanese mobile electronics manufacturer.
- Mitteilungen des Instituts für Orientforschung.
- Michael Mio Nielsen, former Danish footballer.
- Mio Card, a company that sells debit cards for recurring payments.
- MIQ, female Japanese pop and anime theme song vocal artist, who first used MIO as her name.
- Mio, the headclerk from the manga Pick of the Litter
- Mio, my Mio, a book by Astrid Lindgren
- Yamaha Mio, a motorcyle made by Yamaha Motor
Also, mio means mine in Italian, as does mío in Spanish.