"Telefonica has transferred... 1.11 billion ordinary shares in Telecom Italia... to Vivendi," the Spanish firm said in a statement to the Madrid stock exchange.
"Telefonica hereby announces the divestment of its entire shareholding in Telecom Italia."
In return, Vivendi transferred back to Telefonica a 4.5 percent stake that the French company had earlier acquired in Telefonica's Brazilian subsidiary.
The deal was one of a series of transactions in a complex agreement signed on September 19th for Telefonica to take control of Brazilian telecom firm GVT from Vivendi.
Telefonica said the deal overall would yield it a pre-tax gain of €380 million ($426 million).
The deal boosted Vivendi's stake in Italy's biggest telecom provider to 14.9 percent, Bloomberg reported. It said Telefonica sold the shares for about €1.03 billion.
Telecom Italia shares closed 1.09 percent lower at €1.18 euros in trading in Milan on Wednesday.