Sunday's referendum required half of the electorate to cast a ballot in order to be valid. Only 46 percent of voters turned out in 97 percent of polling stations, according to the central election bureau, thereby rendering the vote invalid.
"Romanians have rejected the coup staged by the 256 lawmakers led by [Prime Minister] Victor Ponta and [interim President] Crin Antonescu," Basescu said from his campaign headquarters minutes after polling ended, according to the AFP news agency.
Leftist Prime Minister Ponta, whose cabinet assumed power in Romania in April without elections, launched the referendum process in an attempt to oust Basescu, accusing the president of overstepping his authority.
Ponta's actions raised concern in the West about democratic standards in Romania, and Basescu referred to the impeachment attempt as a coup.
Ponta on Monday said that despite the referendum's failure, Basescu had been rejected by Romanians and would no longer have legitimacy.
"He will remain at Cotroceni [the presidential palace], but he will no longer have legitimacy," Ponta said, pointing out that more than 87percent of those who did cast ballots voted for Basescu to be removed from office.
And Ponta indicated that his government would not cooperate with the president in the future.
"What's there to discuss with a man who has been rejected by Romanians?" Ponta said.
Basescu's popularity dropped as a result of austerity measures he and his allies supported in order to shore up Romania's economy.
tm, ncy/pfd (AFP, dpa)