Saint Theodosia of Constantinople (Greek: Ἁγία Θεοδοσία ἡ Κωνσταντινουπολίτισσα, Hagia Theodosia hē Kōnstantinoupolitissa) is an Eastern Orthodox and Roman Catholic Saint and Martyr who lived in the seventh and eight centuries.
Theodosia was a nun living at a monastery in Constantinople. On January 19, 729, at the very beginning of the iconoclastic persecutions, the Emperor Leo III the Isaurian ordered that an icon of Christ which stood over the Chalke Gate of the imperial palace be removed. While an officer was executing the order, a group of women gathered to prevent the operation. Among them was Theodosia, who shook the ladder strongly until the officer fell from it. The man died from his injuries, and Theodosia was arrested and brought to the Forum Bovis, where she was executed by having a ram's horn hammered through her neck. Following the Triumph of Orthodoxy over iconoclasm she was recognized as a martyr and saint, and her body was kept and venerated in the church of Hagia Euphemia en to Petrio, in the quarter named Dexiokratianai, named after the houses owned here by one Dexiokrates. It corresponds to the modern neighborhood of Ayakapı, along the Golden Horn. After the beginning of the fourteenth century, the church was named after her. It corresponds possibly to the mosque of Gül. Also a gate in the sea walls of Constantinople, the Gate of Hagia Theodosia (Turkish: Ayakapı) was named after her church.