Our correspondent says past logging contracts were corruptly agreed
The Democratic Republic of Congo government has cancelled nearly 60% of timber contracts in the world's second-largest tropical rainforest.
It follows a six-month review of 156 logging deals aimed at stamping out corruption in the sector and enforcing legal and environmental standards.
At the end of the World Bank-backed process, government ministers found that only 65 timber deals were viable.
New contracts will be issued for 90,000 sq km (35,000 square miles) of forest.
Environment Minister Jose Endundo told a news conference in the capital Kinshasa that the other agreements would be cancelled.
"I will proceed within the next 48 hours to notify those applicants having received an unfavourable recommendation from the inter-ministerial commission through decrees cancelling their respective conventions," he was quoted as saying by Reuters news agency.
"Upon notification of the cancellation decision, the operator must immediately stop cutting timber."
Mr Endundo also said the government planned to respect a moratorium, introduced during Congo's 1998-2003 war but widely ignored, on granting new logging deals.
The BBC's Thomas Fessy in Kinshasa says all the timber agreements were struck during the conflict.
Amid rampant corruption, huge concessions were gifted to logging companies, which paid almost no tax, he says.
Monday's decision should reduce the surface area exploited by timber firms by up to half, according to our correspondent.
The Congo Basin is home to the second largest tropical forest in the world after the Amazon, but campaigners say it is being eaten away by logging, mining and agricultural land clearance.
Sarah Shoraka, of Greenpeace, says the new rules must be enforced to protect a vital resource.
"Real economic development is what's needed," she told the BBC's Focus on Africa programme.
"We've highlighted tax evasion, and there's often quite serious disputes between local people and these logging companies.
"The logging companies promise hospitals and schools and they hardly ever deliver these things on the ground."