The work, budgeted at 705.6 million reais ($398 million) started with the removal of the seats in the lower ring of the stands in the stadium, the likely venue for the final.
Renovations will see the stadium's capacity reduced by more than half to 45,000 for the next 50 days and then closed.
The work is scheduled to be completed by Dec. 31, 2012, in time to stage the Confederations Cup in Rio the following year.
Maracana work for 2014 World Cup gets underway late
August 25, 2010