The Brazil international has signed a three-year contract with the Giallorossi.
"I am convinced we'll have a great season. I'm happy with the warm welcome from the fans, as they were looking for me all over the city.
"I don't like making promises, but I know what I must do on the pitch and I say it will go well."
A statement from the club confirmed the contract will expire on June 30 2013 and is worth 5m per season, plus performance-related bonuses.
The return to Serie A is something few expected when he walked away from Inter in April 2009 while suffering from depression.
"This is something I really care about and the reason I came back to Italy. I am here and must prove what I can do. I will do it.
"I am ready to take on Inter."