Isthmia may refer to:
- Isthmia (sanctuary) at the east side of the Isthmus of Corinth, Greece
- The ancient Isthmian Games, held at the sanctuary
- Temple of Isthmia, located in the sanctuary
- Isthmia, Corinthia, a village in the municipal unit Loutraki-Perachora, Corinthia, Greece, near ancient Isthmia
- Isthmia (genus), a genus of diatom in the Coscinodiscophyceae subclass