The Brazilian midfielder is happy to be back with the Serie A giant after spending the past four years at Real Madrid.
The Brazilian midfielder left Milan for Real Madrid for 65 million euros in the summer of 2009, but now rejoins the Rossoneri on a free transfer after he was deemed surplus to requirements by the Santiago Bernabeu side.
"I am returning home again," Kaka told Sky Sport Italia following his confirmed move to Milan. "I am very happy to be back at Milan.
"We have a great team. I can't wait to play at San Siro again and feel the same emotions from before. I will be wearing the No.22 jersey again."
The 31-year-old made nearly 200 Serie A appearances for Milan between 2003 and 2009, winning one league title in the process.