The Battle of Olpae was a battle of the Peloponnesian War in 426 BC, between armies led by Athens and Sparta.

In 426, 3,000 hoplites from Ambracia invaded Amphilochian Argos in Acarnania on a gulf of the Ionian Sea and occupied the fort of Olpae. The Acarnanians asked for help from both the Athenian general Demosthenes, and the 20 Athenian ships located nearby under the command of Aristotle and Hierophon. The Ambraciots asked for help from Eurylochus of Sparta, who managed to march his army past the Acarnanians without being observed. After this, Demosthenes arrived in the gulf below Olpae with his ships, 200 hoplites, and 60 archers. He joined with the Acarnanian army and set up camp in a ravine opposite Eurylochus, where both sides made preparations for five days. As the Ambraciot and Peloponnesian army was larger, Demosthenes set up an ambush with 400 hoplites from Acarnania, to be used when the battle began.