Ostoja (Serbian Cyrillic: Остоја) may refer to:
- Ostoja, Łódź Voivodeship, a village in Poland
- Ostoja, West Pomeranian Voivodeship, a village in Poland
- Clan of Ostoja, a late medieval European clan
- Ostoja coat of arms
- Ostoja, masculine given name
- Ostoja Rajaković, Serbian medieval nobleman
- Ostoja Stjepanović, Macedonian footballer
- Stephen Ostoja of Bosnia, Bosnian king