Ahter Kutadgu, head of corporate communications for Turk Telekom, told the Anatolia news agency his company had been notified of a court decision to lift the ban.
Kutadgu did not elaborate on the court's reasoning.
"As soon as the court decision lifting the ban reached us, we immediately opened YouTube," he said.
The Istanbul court that ordered the site blocked on Wednesday had said it would lift the ban as soon as it ascertained that videos insulting Turkey's founding father, Mustafa Kemal Ataturk, were removed.
The ban had been condemned by the press freedom group Reporters Without Borders and drew attention to Turkey's shaky record on permitting free expression.
It is illegal in Turkey to insult Ataturk, a revered figure whose image graces every denomination of currency and whose portrait hangs in nearly all government offices.
Several prominent Turkish journalists and writers have been tried for allegedly insulting Ataturk or for the crime of insulting "Turkishness."
