Preliminary results suggest that Evo Morales will face Carlos Mesa in the second round of the presidential election in December.
With more than 80 per cent of votes counted, Morales was in front with 45 per cent followed by Mesa's 38 per cent.
The announcement was made by the country's election authority in La Paz in the early hours of Monday morning.
Reacting to the vote, Morales refused to concede there would be a second round when addressing supporters from the steps of the presidential palace.
"Another triumph, we won again, we won four consecutive elections in Bolivia," he said.
Morales is hoping for a large turnout from rural voters, who have traditionally backed his Movement towards Socialism (MAS) party.