In a secret ballot of 1,010 parliamentarians and regional representatives, no one secured the two-thirds majority required in the first three ballots to elect Italy's president, provisional results showed.
A second and if necessary third round will be held on Tuesday. By the fourth ballot, which would be held on Wednesday, a simple majority would be sufficient.
Silvio Berlusconi, the outgoing prime minister refused to support Romano Prodi's candidate. Prodi, the incoming prime minister, who cannot take office until a president is elected, had proposed Giorgio Napolitano, 80, as a compromise after Berlusconi said he would not accept a more high-profile left-wing politician.
The electors began voting at 4.25pm (1425 GMT) to choose a successor to President Carlo Azeglio Ciampi, whose seven-year term expires this month.
Sortly before the vote, Berlusconi said his centre-right bloc would vote for his closest political aide, Gianni Letta.