 As Schalke 04 terminated his contract in December 2015, Boateng re-joined Milan on 5 January 2016 on a free transfer and signed a six-month contract.He was training with Milan since his suspension in September 2015.He made his official return debut on 9 January 2016, playing 36 minutes against Roma in a 1–1 draw and scored his first goal in his first match back at the San Siro six days later against Fiorentina in a 2–0 win.