While eight candidates are in the running, the election is being seen as a race between indigenous peasant leader Evo Morales, 46, and US-educated former president Jorge Quiroga, 45.
On election day Mr Morales reiterated his pledge to increase state controls over Bolivia's key gas resources and to protect plantations of coca, the base
ingredient of cocaine, which is also used in religious ceremonies and to combat
altitude sickness in the Andean country.
Should he win the election, "there will be zero cocaine, zero narco-trafficking but not zero coca," Mr Morales said after casting his ballot in Villa Tunari, in the heart of Bolivia's coca-growing region.
He also said his government would cooperate closely with other "anti-imperialists," a reference to Venezuelan President, Hugo Chavez, and Cuban President, Fidel Castro, the most passionate anti-US leaders in Latin America.
Mr Morales reiterated his admiration for Cuba's communist leader.
"I have a lot of respect for Fidel and the Cuban people," he said.
Different visions
The two frontrunners offer radically different visions for Bolivia, a
landlocked country that is roughly twice the size of France.
Mr Morales has led popular protests over social and economic policies and
played a key role in the collapse of two governments. His campaign was marked
by anti-US slogans.
Should he be elected, Mr Morales would become the first indigenous president
in a country whose political system has been dominated for centuries by descendants of European immigrants.
His pledges to increase state control over the natural gas industry and to roll back coca eradication efforts have raised concerns Washington could end preferential trade agreements and drop aid to Bolivia, South America's poorest country.
Mr Quiroga, who served as interim president for a year from 2001, is seen as a pro free-market technocrat. He wants to boost ties with the United States and attract more private investment.
Exit polls
Exit polls after the election showed Mr Morales winning far more support than anticiapted but not enough to win outright without going to a second round.
The polls, conducted by the Mori and Isos-Captura institutes, both showed Mr Morales getting 44.5 per cent of the votes and Mr Quiroga garnering 34 per cent.
Voters
About 3.6 million voters were called to cast ballots in the elections that
will also renew the 130 deputies and 27 senators of the legislature.
The newly-elected lawmakers may be the ones who will end up picking the
president.
Should none of the candidates get 50 per cent of the votes, Congress must decide next month which of the top two vote-getters will become the new president.