It is the first attempt to hold a poll since failed elections in 1992, but European Union observers have already started to cast doubt on efficiency, describing the organisation of the poll as a "disaster".
In the 1992 election, Jonas Savimbi, the former Unita leader, withdrew from the second round of a presidential poll after accusing Dos Santos of rigging.
The country's civil war then resumed until Savimbi was killed in an ambush in 2002.
Since the war, oil production has more than doubled, fuelling economic growth in double digits.
Despite this, the country suffers massive unemployment and poverty. Two-thirds of Angolans live on $2 a day and at least 40 per cent of the workforce is unemployed.
|The MPLA hopes to win a two-thirds majority in parliament [AFP]
Isaias Samakuva, the leader of Unita, said: "After so many years of [MPLA] government, people are still poor. I'm sure that a lot of Angolans would like to see their lives improve."
In an apparent admission of failings on the government's part to distribute the oil wealth, Dos Santos pledged change at a final campaign rally on Thursday.
"For us, change does not necessarily come about by a change of party. To change public policies which haven't worked ... we must change the members of the team who are bad," he said.
The MPLA says it is the only party capable of continuing the rebuilding of the capital, Luanda, and the provinces, where years of war destroyed communication systems and roads.
In the election, the party hopes to boost its share of the 220-seat parliament, possibly winning a two-thirds majority that would allow it to institute sweeping constitutional changes.
The MPLA held 129 seats going into the election, with the remainder mostly controlled by Unita.
Delays and intimidation
Luisa Morgantini, head of the EU election observer mission, said: "What we have seen at three polling stations we have visited in Luanda is a disaster. They did not prepare."
Voters formed long lines queueing to cast their ballot in white tents erected as polling booths.
Unita has alleged intimidation and bias from the ruling party during the month-long campaign leading up to the poll.
Human rights groups have also criticised the campaigning as unfair, as the MPLA received massive state funding and media coverage.
"The system in which these elections were organised is not fair ... this campaign was very unbalanced," Samakuva, said.
The government has denied the opposition's allegations and said that it is doing all it can to rebuild the nation after six years of peace.
Friday was declared a national holiday to enable voters to get to the polls.