Sphacteria is a small island at the entrance to the bay of Pylos in the Peloponnese, Greece. Its modern name is Sphagia.

In ancient times it was the site of the Battle of Sphacteria in the Peloponnesian war. In modern times the bay was the site of the Battle of Navarino in the Greek War of Independence from the Ottoman Empire (the forerunner to modern-day Turkey).