At stake are 120 elected seats, with President Robert Mugabe appointing an additional 30 seats.
"We have come to make a statement," said one young man, grinning as he headed towards a polling station in Harare.
There was no visible police presence in the centre of the city but witnesses said there were some patrols in outlying townships where there have been anti-government protests in the past.
Mugabe, 81, told loyalists of his Zanu-PF party on Wednesday that the poll would be fair and urged voters to reject the opposition Movement for Democratic Change (MDC), which he calls a puppet of British Prime Minister Tony Blair.
Zanu-PF is widely tipped to win the parliamentary poll. The MDC, despite crying foul even before polls opened, put on a brave face.
"The MDC is confident of victory," MDC Secretary-General Welshman Ncube said in a statement on Wednesday.
"The people are behind us. If the MDC does win the election it will be because the will of the people will have prevailed over attempts by Mugabe and Zanu-PF to rig the ballot."
Nevertheless, the MDC appears weaker than in the last two elections, when it came close to achieving shock victories.
"We are not anti-white, but we are anti-racism"
The MDC and Western observers say both those votes were rigged. Thursday's election has already been branded unfair by both the United States and the European Union.
The EU blasted the polls as "phoney" and warned it would take unspecified steps against Zimbabwe after the election.
Mugabe says Washington and European governments led by former colonial power Britain want to topple him because of his seizure of white-owned land for landless black Zimbabweans.
Critics blame the land seizures, which began in 2000, for ruining the commercial farming industry, leaving the once prosperous country short of food and triggering a wider economic collapse that has seen inflation and unemployment skyrocket.
Mugabe, who has led the former Rhodesia since independence in 1980, denies his mismanagement is to blame and accuses Western and domestic opponents of conspiring to sabotage the economy.
On Thursday he defended the land redistribution programme, telling supporters at his closing rally: "We are not anti-white, but we are anti-racism."
"If the MDC does win the election it will be because the will of the people will have prevailed over attempts by Mugabe and Zanu-PF to rig the ballot"
A clear victory would keep Zanu-PF firmly in control as its ageing leader approaches planned retirement in 2008.
The party hopes to win back urban voters who rejected it in parliamentary and presidential votes in 2000 and 2002, while the opposition MDC, which emerged from urban trade unions, has tried to broaden its support in rural districts.
Mugabe has come under regional pressure to abide by new election standards adopted last year by the Southern African Development Community, and although the MDC says Zimbabwe falls far short of full compliance, the opposition party says violence this time has been much reduced compared to 2000 and 2002.
Results are expected within 48 hours of polls closing.