Romania's election rules stipulate the referendum needed a turnout of more than 50 percent of eligible voters to be valid. However, with 97.5 percent of the votes counted, the Central Election Bureau Monday pegged turnout at 46.13 percent, The New York Times reported.
Of those who voted, about 87.5 percent cast ballots to impeach Basescu, the bureau said.
International leaders have criticized tactics, such as the referendum, used by Basescu's rival, Prime Minister Victor Ponta, to try to drive the president from power.
Ponta Monday said Basescu had been discredited and questioned the president's authority after the "massive vote" against him.
Basescu, 60, hailed results Sunday, saying "Romanians rejected a coup d'etat. ... The flame of democracy is still burning."
Basescu said he recognized he had lost popular support and promised to work for reconciliation.
Romania, among the poorest countries in the European Union, has struggled to conquer lawlessness and corruption since joining the bloc in 2007. Critics say Ponta's ruling coalition has undercut democracy by ousting the speakers of both parliamentary chambers and replacing the country's ombudsman, who can challenge emergency legislation before the Constitutional Court.
Ponta and his supporters said the referendum was justified against a president they accuse of abusing his power. Ponta has said Basescu violated Romania's constitution by using the country's secret services against his enemies, refusing to appoint ministers chosen by the prime minister, pressuring prosecutors in criminal cases and illegally tapping phones.
Basescu denied the accusations.
Basescu is tied to unpopular austerity measures taken after Romania sought emergency loans from the International Monetary Fund following the beginning of the recession in 2009.