London: The Blues have landed the Internacional attacker following their pursuit of the 20-year-old throughout the summer, as the Champions League winners' make their fourth signing of the window.
Chelsea have not revealed the transfer fee - though it is widely reported to be in excess of 25 million pounds.
Oscar, full name Oscar dos Santos Emboaba Junior, is a product of the Sao Paulo youth set up. He left the capital for Internacional in Dec 2010 and has played at every level of international football from Under-15 to Under-20.
The Blues have landed the Internacional attacker as Chelsea make their fourth signing of the window.
He is Chelsea's fourth signing of the summer, joining Marko Marin and brothers Eden and Thorgan Hazard at Stamford Bridge. He scored 13 goals in 44 matches in all competitions last season.