Sylvester (or Silvestros) Syropoulos (Greek: Σίλβεστρος Συρόπουλος; c. 1400 – aft.
1464) was a Byzantine official, the grand ecclesiarch (megas ekklesiarches) of the Hagia Sophia and the dikaiophylax of the Patriarchate of Constantinople.
Upon his return to Constantinople, he claimed to have acted under duress and disavowed the union.
He became a supporter Archbishop Mark of Ephesus, leader of the anti-unionist movement.
In 1443, he composed his Memoirs (Ἀπομνημονεύματα, Apomnemoneumata), an important first-hand account of the council, especially of its behind-the-scenes intrigue.