Former Bolivian leader Jorge Quiroga has withdrawn his presidential candidacy just a week ahead of the vote.
Quiroga wrote on Twitter on Sunday that he had no prospect of winning and wanted to prevent a sweep by ex-president Evo Morales' left-wing MAS party in the first round of voting.
Interim president Jeanine Anez also recently withdrew her running for the country's highest office, saying she hoped it would prevent the conservative vote being split between too many candidates, which would likely lead to an MAS victory.
Recent polls showed Quiroga with 1.1 per cent of the vote.
MAS candidate Luis Arce was at 33.6 per cent, former president Carlos Mesa at 26.8 per cent and right-wing civic leader Luis Fernando Camacho on 13.9 per cent.
To win the first round of voting, a candidate needs over 50 per cent of votes or more than 40 per cent of votes and a 10 percentage-point lead against the second-place candidate.
The elections are a rerun of last year's poll, in which Morales, the Andean country's leftist president of 13 years, claimed victory.
Widespread allegations of fraud sparked weeks of violent protests that forced Morales, Bolivia's first indigenous president, into exile.
Anez, a conservative, took power as interim president.
Australian Associated Press