The OAS approved suspending Honduras by 33 votes to zero, with Honduras itself not voting.
It was the first time the organisation had taken such a measure since Cuba was suspended in 1962, when it allied itself with the USSR.
Warning
Mr Zelaya was forced to leave the country by the military as he pressed on with plans to hold a non-binding public consultation on 28 June, to ask people whether they supported moves to change the constitution.
On Saturday, he again said he intended to defy his country's new government by returning home.
"I am organising my return to Honduras... This is the return of the president elected by the sovereign will of the people," he said, saying he would arrive between 1300 and 1400 local time (1900 to 2000 GMT).
He called on his followers to join him "without arms" on his arrival in the capital, Tegucigalpa.
He said he would be accompanied by President Cristina Fernandez de Kirchner of Argentina and Rafael Correa of Ecuador.
Thousands of his supporters are expected to be at the airport.
Mr Zelaya also warned the new administration of interim leader Roberto Micheletti that the international community had turned against them.
"Your actions will not go unnoticed because the international courts will have to try you for the genocide that you are carrying out in our country, in suppressing rights and repressing our people," he said.
The Honduran interim government says it acted within the law and has the backing of the majority of the population.
Church warning
Earlier, the leader of the Roman Catholic Church in Honduras called on the ousted president not to return from exile, in order to avoid provoking what he called a "bloodbath".
Cardinal Oscar Rodriguez said nobody had been killed since Mr Zelaya lost power, and he appealed to him to check his actions before it was too late.
The country is becoming increasingly polarised, our correspondent says.
Each day there are mass demonstrations, both in support and against the government.
Mr Zelaya, a wealthy businessman, is a left-wing politician and supporter of Venezuelan President Hugo Chavez.
His opponents, which includes the Supreme Court and a majority in Parliament, accuse him of seeking to prolong his rule.
He had wanted to hold a popular vote on convening a constitutional convention - a move that could have removed the current one-term limit for presidents.
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