The relic was discovered during excavations at the Balatlar Church in the northern province of Sinop near the Black Sea, Turkish news agency 'Anadolu' reported.
Professor Gulgun Koroglu, an art historian and archaeologist at Turkey's Mimar Sinan University of Fine Arts found a stone with crosses carved in it.
"We have found a holy thing in a chest. It is a piece of a cross, and we think it was [part of the cross on which Jesus was crucified]," said Koroglu who headed the excavations.
The chest has been sent to a laboratory for further examination, NBC News reported.
Koroglu said her team has been working since 2009 at the church - which was built in the year 660, during the Byzantine era.
She said the ruins of an ancient Roman bath were also found at the site, along with more than 1,000 human skeletons.