Milan were keen to snap up the forward to appease their fans having lost stars such as Thiago Silva and Zlatan Ibrahimovic during the close season.
“I chose Milan for many reasons,” said Krkic, who joined Roma for 12 million Euros from Barca a year ago.
He scored seven goals in 33 appearances for Roma last term.
"It (Milan) is a great club and the team is made of an historic group of players," he added. "I want to thank the coach, who wanted me so much, by playing at my best.”
- Zlatan Ibrahimovic