Officials said turnout had been high, although opposition parties disagreed
Ethiopia's ruling party has won all but a handful of local council and parliamentary seats following an opposition boycott of the April poll.
The EPRDF regained control of the capital Addis Ababa and won all but one of the 39 parliamentary by-elections.
Many of the seats were declared vacant after opposition leaders who had won them in 2005 were arrested over protests at alleged electoral fraud.
These were the first polls since the protests, in which 200 people died.
Lobby group Human Rights Watch said thousands of opposition candidates and prospective voters had been threatened, attacked and arrested during campaigning for the polls.
The EPRDF won more than 3.5 million of the 3.6 million seats, reports the AFP news agency.
The electoral commission said turnout was 93%.
But the leader of the opposition Oromo Federalist Democratic Movement (OFDP), Bulcha Demeksa, said there had been a very low turnout.
Mr Bulcha said his party had only been able to put forward 2% of the 6,000 candidates it wanted to because they had been threatened by government supporters.
In the 2005 elections, candidates fighting under the banner of the Coalition for Unity and Democracy (CUD) won a landslide victory in Addis Ababa, but the polls were followed by violent protests.
The CUD's leaders were arrested and spent most of the intervening period in jail.
Though now free, they were unable to register in time for the elections.