About 4,500 candidates are standing in the election.
The polls open at 0430 GMT and are to remain open till 1930 GMT.
Initial results from Tehran are expected to come in by late Saturday or Sunday, however, Iranian officials said that the final results would not be announced until several days after the voting.
Senior officials and state media have made every effort to encourage a massive turnout as a display of national unity.
State television has been repeatedly playing patriotic music and pictures of long queues of people voting in past elections, as well as running interviews with ordinary and famous Iranians emphasising the importance of voting.
"Iranians will take part in the elections more gloriously than the past and will thwart plots of bullying powers to undermine the Islamic system," Ayatollah Ali Khamenei,Iran's supreme leader, said in a speech.
However, Saeed Mohammad Marandi from the University of Tehran told Al Jazeera that the voter turnout would be low despite the extensive advertising.
"The elections are very close to the Iranian New Year, so there is not a great deal of interest in the elections, at the first place," he said.
"The voting process is quite complicated as you do not vote for your local MP, but for all the candidates in Teheran.
"And it is very difficult to know all the candidates at the same time."
Voting turnout is expected to be around 50 to 60 per cent, which is similar to that of the 2004 elections.
The elections are being considered as a 'litmus test' for Ahmadinejad, who has been accused of failing to control inflation and increasing tensions over Iran's nuclear ambitions, ahead of presidential elections in 2009.
Inflation in Iran has increased by 20 per cent and almost one in 10 people remain unemployed.
Sanctions imposed by the United Nations have weakened Iran's social structure and many are finding it hard to earn a living.
"I would like to see Ahmadinejad and the people in the parliament cope with the money I have," one Iranian told Al Jazeera.
"I would be more than happy to let them have all my salary and see if they could survive on it."
The Iranian parliament wields a good deal of power but its capacities are limited by the unelected Guardians Council, which must approve all of the parliament's legislation.
Source: Al Jazeera and agencies