Mother Cathedral of Holy Etchmiadzin is a 4th century Armenian church in the town of Ejmiatsin, Armenia. It is also the central cathedral of the Mother See of Holy Etchmiadzin of the Armenian Apostolic Church.

Etchmiadzin Cathedral is listed among the UNESCO World Heritage Sites.

The Etchmiadzin Cathedral is the oldest state-built church in the world. The original vaulted basilica was built in 301-303 by Saint Gregory the Illuminator when Armenia became the first officially Christian country in the world. Gregory had converted King Tiridates III and members of his court.

According to the 5th-century Armenian annals, St. Gregory had a vision of Christ descending from heaven and striking the earth with a golden hammer to show where the cathedral should be built. Hence, the patriarch gave the church and the city the new name of Echmiadzin, which may be translated as “the place where the Only Begotten descended”.

In 480, Vahan Mamikonian, the Sassanian governor (marzban) of Armenia, ordered the dilapidated basilica to be replaced with a new cruciform church.

In 618, the wooden dome was replaced with a stone one, resting on four massive pillars linked to exterior walls by arcades. This was the church much as it is today.

Murals in the interior and extravagant rotundas surmounting the apses appeared in the early 18th century. A three-tier belfry was constructed half a century earlier.

The cathedral formerly boasted the largest collection of Armenian medieval manuscripts, but these were lately handed over to the Matenadaran in Yerevan.