Euchaita (Εὐχάϊτα) was a Byzantine city and diocese in Helenopontus, the Armeniac Theme (northern Asia Minor), and an important stop on the Ancyra-Amasea Roman road.

Euchaita gained prominence during the later Roman and Byzantine periods as a significant cultic center for the veneration of Anatolian saint Theodore Tiron. Between the 7th and 11th centuries, following the early Muslim conquests, it transitioned into a military outpost. However, with the Turkish conquest of Anatolia in the late 11th century, Euchaita's importance diminished. In Ottoman times, Euchaita was mostly depopulated, but there was a remnant village known as Avhat or Avkat.

Today the Turkish village Beyözü, in the Anatolian province of Çorum (in the subprovince of Mecitözü, Turkey), partly lies on the ruins.

Euchaita, in the Roman province of Helenopontus (civil diocese of Pontus) is known mostly due to its role as a major pilgrimage site dedicated to Saint Theodore of Amasea (martyred c. 306).

Its episcopal see was originally a suffragan (no incumbents known) of the Metropolitan of the provincial capital Amasea, in the sway of patriarchate of Constantinople. In the 5th century, the town was a favourite site of exile for disgraced senior churchmen. In 515, the unfortified town was sacked by a Hunnic raid, after which it was rebuilt, fortified and raised to the status of a city by Anastasius I Dicorus (r. 491–518).

It became an autocephalous archbishopric in the early 7th century, as attested by the Notitia Episcopatuum edition of pseudo-Epiphanius, from the reign of Byzantine emperor Heraclius I (circa 640). The city was burned down by the Sassanid Persians in 615, and attacked by the Arabs under second Umayyad Caliph Mu'awiya I in 640. A second Arab attack captured the city in 663; the raiders plundered the city, destroyed the church of St. Theodore, and wintered there, while the population fled to fortified refuges in the surrounding countryside. The city was rebuilt and soon recovered. The Arabs scored a victory in its vicinity in 810, taking captive the local strategos of the Armeniac Theme and his entire treasury.

A hagiography of the 8th or 9th century claims that the relics of Saint Theodore were at this time still located at Amaseia, but that the Christians of Euchaita with increasing persistence were asking for their transfer to their own city, claiming that this had been the wish of the saint himself when he was alive. Euchaita became a full metropolitan see under Leo VI the Wise (r. 886–912) and Patriarch Photius of Constantinople, ranking 51st among the Metropolitanates of the Patriarchate, with four suffragan sees : Gazala, Koutziagra, Sibiktos and Bariané, but apparently lost them all no later than the 10th century.

In 972, Emperor John I Tzimiskes renamed the neighbouring Euchaneia, whose exact relation or identity with Euchaita is unclear, into Theodoropolis. The town is recorded as having a vibrant fair during the festival of St. Theodore in the middle of the 11th century. After the Battle of Manzikert (1071), Euchaita was at the frontier of the Turkish conquest, and there are no more records about its fate. The settlement was most likely depopulated, and from the 12th century, it was within the Seljuk Sultanate.