The Datafolha survey published today finds 30 per cent of respondents giving positive marks to Rousseff's government, down from 57 per cent registered in its previous poll before the demonstrations began.
Datafolha says it's the biggest drop in a president's approval rating since a 1990 fall for then-President Fernando Collor de Mello, who was forced from office because of a corruption scandal.
The recent protests first targeted transportation fare hikes and quickly expanded to a variety of causes including government corruption, high taxes, poor public services and billions of dollars spent for next year's World Cup soccer tournament.