The Battle of Cnidus (Greek: Ναυμαχία της Κνίδου) was a military operation conducted in 394 BC by the Achaemenid Empire against the Spartan fleet during the Corinthian War.

According to Isocrates, King Evagoras I of Cyprus contributed the greatest part of the forces under Conon for the sea fight off Cnidus.

Following his victory, Conon raided the coast of the Peloponnese with Pharnabazus in order to put pressure on Sparta, and then was sent with his fleet to Athens, where he supervised the rebuilding of the long walls, which had been destroyed at the end of the Peloponnesian War.

According to Pausanias, Conon commemorated the victory by establishing a sanctuary of Aphrodite (the patron goddess of Cnidus and a key deity for the Phoenicians) in Piraeus.

The Peace of Antalcidas in 387 BC officially ceded control of these areas to Persia; it would continue to hold them until the arrival of Alexander the Great half a century later.