Ostia may refer to:
- Ostia (Rome), a municipio (also called Ostia Lido or Lido di Ostia) of Rome on the Tyrrhenian Sea coast
- Ostia Antica, a township and port of ancient Rome
- Ostia Antica (district), a district of the commune of Rome
- ostium, the singular form of ostia, an opening or orifice in Biology
- A song by Sepultura from their Dante XXI album
- A song by Coil from their Horse Rotorvator album
- A fictional region of the country Lycia in Fire Emblem (video game)
- A fictional city in the Magic World in Negima