Brazilian exports of genetically modified organisms, such as soyabeans, will bear the label "contains GMOs" within four years, the environment ministry said late Monday.
Brazil's support of the stronger labelling position marks a shift in its position from the weaker "may contain GMOs" - as is called for by a UN treaty, the Cartagena Protocol.
Brazil signed the Cartagena Protocol, which went into effect in 2003 and aims for greater transparency and control of global GMO trade.
Over 130 other countries signed the treaty and are meeting this week in Curitiba, Brazil, to discuss economic liability and documentation of GMO shipments under the protocol.
Other large GMO exporters, such as the United States, Argentina, Canada and Australia, have not signed the protocol, fearing that it would allow importing countries in regions like Europe to use it as a de facto trade barrier.
Under the treaty's provisions, a country may reject GMO imports if it fears they pose a danger to traditional crops, undermine local cultures or cut the value of biodiversity, even without scientific proof.
Brazil's agricultural sector has been opposed to the stronger wording on the ground that it may hurt local exports of soyabeans or corn to GMO sensitive countries in Europe, Africa and Asia, as well as raise costs. But environmentalists and the European Union have been insisting on more definitive wording on GMO exports.
"The decision of the Brazilian government is a great victory for the biosafety of the planet," Greenpeace in Brazil said in a statement.
Brazil's environment ministry said President Luiz Inacio Lula da Silva reached a decision to support the stronger wording on GMOs with the environment and agriculture ministries.
Brazil's position will be presented in Curitiba this week. Under the proposal, Brazil's grain export sector will have four years to install infrastructure to segregate GMO from conventional grains and set up GMO labelling and testing procedures. Until that time, "may contain GMOs" will be used on GMO exports, the environment ministry said. The protocol applies only to exports and imports and does not apply to domestic trade in GMOs.