Holy Trinity Greek Catholic Cathedral in Istanbul (Turkish: Ayatriada Rum Katoliki Kilise), also called Holy Trinity Rum Catholic Church, is the cathedral of the Greek Byzantine Catholic Church in Istanbul, Turkey. It is located on Hamalbaşı Caddesi in the Beyoğlu district of Istanbul and is currently used as a church for the local Chaldean Catholic community.
It is the main church of the Greek Apostolic Exarchate of Istanbul (Exarchatus Apostolicus Constantinopolitanus) which was created in 1911 with parts of the territory of the Ottoman Empire and since 2016 has been administered by an apostolic administrator. According to the 2017 Annuario Pontificio, it was the sole parish of the exarchate and has 16 parishioners. The cathedral facilities are being used by Chaldean Catholic refugees from the Eparchy of Diyarbekir.
