Opposition leaders claim the vote will be rigged and are already planning demonstrations on Sunday to pressure the government to overturn the results.
Cuts in assistance
About 2.3 million of Armenia's three million people are registered to vote in elections for 131 seats in the national assembly.
Hundreds of local and international observers are monitoring the vote, including more than 300 from the Organisation for Security and Cooperation in Europe.
The US and EU have repeatedly warned of negative consequences if no improvement is seen over past elections, including potential cuts of foreign aid and the scaling back of relations.
Cuts in foreign assistance could be disastrous for Armenia, where more than 30 per cent of people live on less than $2 a day.
The election is also seen as a dress rehearsal for a presidential vote due next year after Robert Kocharian steps down at the end of his second term.
The HKK, led by Kocharian's chosen successor, Serzh Sarkisian, the prime minister, is expected to take first place.
Kocharian has called on voters to support pro-government parties, saying that if the opposition comes to power it will bring instability.
Kocharian said on Armenian television: "If the two most important governmental institutions - the president and the parliament - start a confrontation, the people will be the ones to suffer."
Polling will close at 7pm (1500 GMT), with preliminary results expected within 24 hours.