Leaders of South America's Mercosur trade bloc have agreed to admit Venezuela as a full member.
Some business leaders do not welcome Mr Chavez's rhetoric
Venezuelan President Hugo Chavez will now be able to join in trade negotiations with leaders from Brazil, Argentina, Paraguay and Uruguay.
Chavez has long talked of following the dream of South America's liberator Simon Bolivar to create a united continent.
But some fear the left-winger could cause as much discord as unity.
"I give a hearty welcome to a friend," said Brazilian President Luiz Inacio Lula da Silva.
"Mercosur continues to be an engine for economic integration, even more important for our countries."
Some business leaders in Brazil and Argentina are worried that Mr Chavez's anti-American and anti-free trade rhetoric could jeopardise trade talks with the US and Europe.
However, there is a plus side, says the BBC's Tom Gibb in Sao Paulo.
Mercosur has clauses about democracy, and those who mistrust the authoritarian leanings of Mr Chavez would like him to sign up to these, our reporter adds.
In the meantime, the South American countries are keen to take up offers of cheap Venezuelan oil.
One of the first areas of co-operation could be plans to build a gas pipeline uniting South America from Argentina to Venezuela.
The outgoing Mercosur head, Argentina's ex-President Eduardo Duhalde, said Venezuela's entry was "more political than real" for the time being.
Venezuela, he pointed out, already belongs to another South American trading bloc with a completely different tariff regime, and that it will take time for Venezuela to be able to meet Mercosur rules.
Mr Chavez himself said the importance of Mercosur was as much political as economic.
"Mercosur has to be a project of the people," he said.
"It has to be a collective project because we are all Mercosur."