Amarynthos (Greek: Αμάρυνθος, [aˈmarinθos], also called Βάθεια Váthia), is a coastal town and a former municipality in Euboea, Greece.

During the 2nd millennium BC, the Ionians arrived in the southern parts of Greece and settled Euboea, while the name of Amarynthos is mentioned in clay tablets with inscriptions in the Linear B script.

[7] Amarynthos, like the whole of Euboea, was later ruled by the Macedonians, the Romans, the Byzantines, the Venetians and the Ottoman Turks until it joined the modern Greek state around 1830.

The municipal unit Amarynthos is located in Central Euboea and stretches from the coast of the South Euboean Gulf into the mountainous inland.

Worth visiting in Amarynthos are the Byzantine churches of "Koimisi tis Theotokou" (κοίμηση της Θεοτόκου), "Metamorphosi tou Sotiros" (μεταμόρφωση του Σωτήρος) and "Zoodochos Pigi" (Ζωοδόχος πηγή), while to the northeast of the town there is the Byzantine monastery of "Agios Nikolaos" (άγιος Νικόλαος), with wall paintings of the 12th century.

A Macedonian tomb dating from the 4th century BC has been excavated in 1897 one kilometre outside of Amarynthos in a location called Vlychos.