"The show is on again. The prosecutor's office asked the judge to reconsider and she revoked the suspension," a spokeswoman for the Rio Justice Tribunal said.
Rio is the last concert in Saturday's Live Earth global series -- partly organized by former U.S. Vice President Al Gore -- with events also due in London, Sydney, Johannesburg, Tokyo, Shanghai, Hamburg and East Rutherford, New Jersey.
The Rio prosecutor's office had sought an injunction to stop the pop concert on Copacabana beach because too few police would be available as officers prepare for the Pan American Games, which start on July 13 in the crime-plagued city.
But the event's organizers, including the RioTur municipal tourism authority, said they had obtained a police guarantee on Thursday that there would be adequate security.
"We met with authorities and addressed their concerns, and the concert will continue as planned," Kristina Schake, Live Earth's communications director, said in a statement.
Rio is the only Live Earth concert free and open to the public. If it had been stopped, it would have been the second cancellation; Istanbul was dropped last month because of a lack of interest and security concerns. Ticket sales have been slow for most Live Earth shows and organizers had to change venues in Johannesburg in a bid to improve sales there.
A giant beach stage in front of Rio's plush Copacabana Palace hotel was already up. Organizers said they plan to use dozens of observation towers and platforms as well as police cameras in the security plan for the event.
Performers including Lenny Kravitz, Pharrell Williams, Jorge Ben Jor and Macy Gray have been lined up to play on Copacabana to an expected audience of up to 1 million people.
A cancellation would be embarrassing for city officials, who hope the show and the games will showcase Rio's legendary charms instead of exposing its rampant crime.
Rio has one of the highest murder rates in the world, with a toll comparable to some war zones. At least 1,800 people were killed in the first four months of 2007 in the metropolitan area, official figures show.
Police have stepped up operations against drug gangs in Rio's slums in the run-up to the Pan American Games. Last week, they raided a slum on the city outskirts, killing about 20 people after a siege in which two dozen people had been killed and more than 60 wounded since May.
(Additional reporting by Michelle Nichols in New York)
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