Antalcidas (Greek: Ἀνταλκίδας) was a Spartan soldier and diplomat, the son of Leon.
In 393 (or 392) BC he was sent to Tiribazus, Persian satrap of Sardis, to undermine the friendly relations then existing between Athens and Persia, offering to recognize Persian claims to the whole of Asia Minor and supremacy over Greek cities there.
The Athenians sent an embassy under Conon to counteract his efforts. Tiribazus, who was favourable to Sparta, threw Conon into prison, but Artaxerxes II (Mnemon) disapproved and recalled his satrap.
In 388 BC Antalcidas, then commander of the navy went to the active assistance of Persia against Athens. The success of his naval operations in the neighbourhood of the Hellespont was such that Athens was glad to accept terms of peace (the Peace of Antalcidas), by which:
- the whole of Asia Minor, with the islands of Clazomenae and Cyprus, was recognized as subject to Persia
- all other Greek cities—so far they were not under Persian rule—were to be independent, except Lemnos, Imbros and Scyros, which were to belong, as formerly, to the Athenians.
The terms were announced to the Greek envoys at Sardis in the winter of 387/386 BC, and were finally accepted by Sparta in 386. Antalcidas continued in favour with Artaxerxes, until the annihilation of Spartan supremacy after the Battle of Leuctra diminished his influence.
A final mission to Persia, probably in 367, was a failure, and Antalcidas, deeply chagrined and fearful of the consequences, is said to have starved himself to death.