The Theodosius Cistern (greek: Κινστέρνα Θεοδοσίου, turk: Şerefiye Sarnıcı) is one of many ancient cisterns of Constantinople that lie beneath the city of Istanbul, Turkey. The modern entrance is in Piyer Loti Caddesi, Fatih.
It was built by Roman Emperor Theodosius II between 428 and 443 to store water supplied by the Valens Aqueduct. The Aqueduct of Valens was redistributed by Theodosius from its original supply to the Nymphaeum, the Baths of Zeuxippus and the Great Palace of Constantinople. This redistribution led to the construction of the Theodosius Cistern.
The area is about 45 by 25 metres and the roof is supported by 32 marble columns about 9 metres high.
Like the Basilica Cistern and the Binbirdirek Cistern, it is open to the public.