With a conservative sweep a virtual certainty after the disqualification of most reformist candidates, the regime appealed for a massive vote, calling each ballot cast a "bullet into the heart" of US President George W. Bush.
Many pro-democracy leaders, stripped of any chance of retaining control of the 290-seat Majlis, or parliament, hoped for a boycott to discredit the conservative-dominated election process.
The polls closed in mosques, schools and other public buildings at 10:00 pm (1830 GMT) after the interior ministry extended the voting period by four hours to accommodate what it called a "heavy turnout."
But as counting began, there was no clear indication of how many of Iran's 46.3 million eligible voters had cast ballots, interior ministry sources said.
The first results were due Saturday and a definitive tally several days later.
The elections capped a frustrating legislative mandate for the reformists, who captured three-quarters of the Majlis seats in 2000 but saw fundamentalist clerics block proposed changes at virtually every turn.
The conservatives were poised to add the legislature to the other political and security institutions under their tight control, and further erode the power of embattled reformist President Mohammad Khatami.
Iran's deadlocked political system has triggered growing voter apathy. If two-thirds of the electorate cast ballots in the 2000 legislative elections, less than half turned out for local polls last year.
Iran's supreme leader Ayatollah Ali Khamenei was among the first to vote and delivered a broadside at "the enemies (who) are trying hard to stop the people from going to the ballot boxes."
Ayatollah Ahmad Janati, head of the powerful Guardians Council, a hard-line bastion, played upon resentment in the Islamic republic over US charges that the Iranian vote was undemocratic.
Janati told a crowd gathered for Friday prayers at Teheran University that "voting is as important as praying" and each ballot cast was like "firing a bullet into the heart" of Bush, who famously lumped Iran into an "axis of evil".
State television rallied voters with shots throughout the day of long voting queues, patriotic songs, clips of the late revolutionary leader Ayatollah Ruhollah Khomeini and footage from the 1980-1988 war with Iraq.
Khatami, who is limping to the end of his second and final term in mid-2005, also urged Iranians to vote massively and defy forecasts of a victory by the conservatives who have ruled since the 1979 Islamic Revolution.
"God willing, with the massive turnout of voters, we will witness a surprise," the beleaguered chief executive told reporters after casting his ballot in Tehran.
All 290 seats were up for grabs except for the one from the south-eastern city of Bam, devastated by an earthquake in December. A second round of voting may be required if no candidate in a given district wins 25 percent.
The pro-democracy movement swept to its majority four years ago after a noisy campaign that rattled hard-liners determined to prevent the undermining of Islamic values.
But most of their candidates were among some 2,300 barred from standing by the Guardians Council, which rigorously screened prospective MPs for their commitment to Islam and the regime.
In addition, officials said that of the 5,625 approved candidates, 1,179 dropped out.
Reformists in the interior ministry - which is organising the vote - were nevertheless on their toes over fraud, saying they had foiled a plan to bus voters to other constituencies in the south of the country.