He's buying out Mr Bates for £60 million and he's agreed to spend another £80 million clearing the club's debts - bringing the total deal to £140 million.
Mr Abramovich has agreed to plough even more cash into Chelsea.
"We have the resources and the ambition to achieve even more given the huge potential of this great club," he said.
Deep pockets
Mr Bates described his successor as someone "with deeper pockets to move Chelsea to the next level".
Chelsea finished fourth in the Premiership last season, securing a place in the Champions League.
Hear story
Play our penalty game!
Talk about football
Score in the FA Cup quiz!
