Brazilian winger Mancini has completed his switch from Inter Milan to AC Milan on a six-month loan deal.
The former Roma star has an option to make his stay with the Rossoneri permanent at the end of the season.
A statement from AC Milan read: "AC Milan announces the signing of Inter Milan player Amantino Mancini on loan until the end of the season with an option to acquire the player's sporting rights once the loan deal ends.''
Mancini becomes Milan's third signing this month following the arrival of England midfielder David Beckham on loan from Los Angeles Galaxy and Ghanaian forward Dominic Adiyiah from Norwegian club Fredrikstad.
The 29-year-old Mancini has failed to hold down a regular spot at Inter since joining Jose Mourinho's outfit in the summer of 2008. Mancini, who is under contract with Inter until June 2012, has made seven appearances for the Nerazzurri this season.