Robinho was unsettled at Manchester City and spent the second half of last season on loan at Santos.
A statement from AC Milan read: "AC Milan announces it has acquired player Robinho on a permanent deal from Manchester City. The Brazilian player has signed a four-year contract with the Rossoneri club."
The Italian club did not reveal the transfer fee for the 26-year-old.
AC Milan signed Zlatan Ibrahimovic from Barcelona on Monday and Robinho's arrival means the Rossoneri will have a lot of Brazilian flair with Ronaldinho and Alexandre Pato already on the books.
Robinho joined City two years ago from Real Madrid for a British record transfer fee of ¦pound;32.5million, but never lived up to the club's lofty expectations.
Earlier on Tuesday, Robinho expressed his satisfaction about joining the Italian giants.
"I am very happy," he said. "Milan is an excellent club."
Source: PA
Source: PA