Euphron was a tyrant of the ancient Greek city-state of Sicyon between 368 and 364 BC.
Euphron was a citizen of Sicyon, who held the chief power during the period of its subjection to Sparta. In 368 BC the city was compelled by Epaminondas to join the Theban alliance, and though its constitution appears to have remained unchanged, the influence of Euphron was considerably diminished. In order to regain it, he took advantage of the dissatisfaction of the Arcadians and Argives with the oligarchical line of Epaminondas, and representing to them that the supremacy of Lacedaemon would surely be restored in Sicyon if matters continued as they were, he succeeded in establishing democracy. In the election of generals which followed, he himself was chosen, with four colleagues. He then procured the appointment of his own son, Adeas, to the command of the mercenary troops in the service of the republic and he further attached these to his cause by an unsparing use, not only of the public money and the sacred treasures, but of the wealth also of many whom he drove into banishment on the charge of Laconism.
His next step was to rid himself of his colleagues and having effected this by the exile of some and the murder of the rest, he became tyrant of Sicyon. He was not, however, entirely independent, for the citadel was occupied by a Theban harmost, sent there, as it would seem, after the democratic revolution. We find Euphron co-operating with that officer in a campaign against Phlius, probably in 365 BC.
Not long after this, oligarchy was again established in Sicyon, by Aeneas of Stymphalus, the Arcadian general, and apparently with the concurrence of the Theban harmost. Euphron upon this fled to the harbour, and, having sent to Corinth for the Spartan commander Pasimelus, delivered it up to him, making many professions at the same time of having been influenced in all he had done by attachment to the interests of Lacedaemon, to which however little credit seems to have been given.