Opponents of the dam construction said they would not be deterred by the awarding of the tender.
Renata Pinheiro, of the Xingu Vivo movement, said: "We will not be discouraged, we will continue to demonstrate."
The protesters said said they plan to occupy some of the 500sq km of the Amazon rainforest land that Greenpeace estimates would be flooded by the Belo Monte dam.
Indigenous groups and environmental activists have staged several demonstrations in recent weeks, saying the dam is ecologically irresponsible.
They also say it will threaten the livelihood of 12,000 families, most of them Brazilian Indians living on the banks of the Xingu river that would feed the facility.
"We, the indigenous, demand justice and respect," read one placard carried by protesters in front of the National Electric Energy Agency's offices.
The regional justice ministry in the state of Para tried to stall tenders for the project in a ruling, calling the dam "an affront to environmental laws".
It said too many questions remained over how the dam would affect flora and fauna in the region, and what would become of the families who would have to be relocated.
But the project has been defended by the local population who hope to benefit from the estimated 18,000 and 80,000 direct and indirect jobs the government says the project will create.
The government has insisted the dam is essential to its plan to boost energy production in Brazil, Latin America's biggest economy.
For a construction cost of $11.2bn, Belo Monte is expected to be able to produce 11,000 megawatts, which could supply 20 million homes with power.
The dam would be the third-biggest in the world, after China's Three Gorges facility, and Brazil's Itaipu dam in the south.
A Greenpeace spokesman said the government should have used other possible energy sources such as wind power, biomass or solar.
Hydroelectric energy accounts for 73 per cent of the energy produced in Brazil.