An election commission official in Luanda said that the MPLA (People's Movement for the Liberation of Angola) party had won just over 64 percent of vote.
The MPLA, which has ruled since Angola's hard-fought independence from Portugal in 1975, had predicted it would easily win, but the result showed a fall in support from the last election in 2012.
In the run-up to Wednesday's election, the two principal opposition parties, UNITA and Casa-CE, alleged the campaign had not been fairly conducted.
They complained that they had been deprived of media access and that voters in opposition strongholds were forced to cast their ballots at polling stations far from their homes.
Before results were released, the MPLA's central committee spokesman Joao Martins declared in the local media that the party's victory was "unequivocal and virtually unavoidable".
The opposition parties hoped to have tapped into public anger over inflation that peaked at over 40 percent last year, as well as low growth and high unemployment.
Dos Santos's long reign saw the end of Angola's bloody civil war (1975 to 2002) and a post-conflict investment boom as the country exploited its oil reserves.
However, a slump in crude prices in 2014 hit the country hard.