The rate of deforestation in the Amazon has dropped by 45% and is the lowest on record since monitoring began 21 years ago, Brazil's government says.
According to the latest annual figures, just over 7,000 sq km was destroyed between July 2008 and August 2009.
The drop is welcome news for the government in advance of the Copenhagen summit on climate change.
But Greenpeace says there is still too much deforestation and the government's targets are not ambitious enough.
According to the Brazilian space agency, which monitors deforestation in the Amazon, the annual rate of destruction fell by 45%.
Welcoming the news, President Luiz Inacio Lula da Silva described the drop in the level of deforestation as "extraordinary".
He said climate change was the most challenging issue the world was facing.
The Brazilian government will undoubtedly view the latest figures as a boost to its green credentials coming just before the Copenhagen summit in December.
At the summit, the Brazilian government seems certain to present its efforts to reduce destruction in the Amazon as a key part of its strategy to combat climate change.
The environment ministry here is said to be proposing that around half of a 40% cut in Brazil's carbon emissions would come from reducing deforestation.
The Brazilian government wants to see an 80% reduction in the deforestation rate by 2020.
The environmental pressure group, Greenpeace, welcomed the latest drop as important, but said that there was still too much destruction in the rainforest.
In a statement, it said the president would be happy if, in 11 years time, the Amazon was being destroyed at a rate of a little less than three cities the size of Sao Paulo a year.
Some environmentalists believe that the fall in deforestation may be connected to the economic downturn, and that when things improve, the Amazon could face renewed pressure.