Constantius I of Constantinople (Greek: Κωνστάντιος; 1770 – 5 January 1859) was Ecumenical Patriarch of Constantinople during the period 1830–1834.

[1] He studied in the Patriarchal School, in Iași and in Kiev.

In 1805, he was elected Archbishop of Sinai, a position he held until he was elected Ecumenical Patriarch in 1830.

He resigned in 1834 and devoted his life to studying and writing.

[2] This article about an Eastern Orthodox bishop is a stub.