Wednesday's controversial election is the second to be held since the war broke out in 2011. More than 388,000 people have been killed and half of the population forced to flee.
Election posters glorifying the authoritarian president have been put up around the two-thirds of Syria controlled by the government.
Voting takes place in 12,000 polling stations and the result is expected on Friday.
Called to vote
Representatives from the regime's powerful security apparatus have called on government employees to vote, according to information to the news agency AFP.
- We have been told to go to the polls or take the consequences, says Jafaar, a government employee in Latakia, who does not want to give his full name for fear of reprisals.
In Damascus, hundreds of students stood in line to vote on campus on Wednesday morning.
Some chanted "with our blood and our souls we sacrifice our lives for you Bashar".
- We have come to elect President Bashar al-Assad.
Without him, Syria would not be Syria, says nursing student Amal.
The 55-year-old al-Assad is facing former minister Abdallah Salloum Abdallah and Mahmoud Merhi, a member of the so-called "permissible opposition" whom opposition leaders in exile have described as an extension of the regime.
International criticism
Last week, thousands of Syrian refugees and expatriates voted in embassies.
But Syrians who fled without getting an exit stamp in the passport were not allowed to vote.
The fighting has largely subsided, but the economy is in free fall.
Over 80 percent of the population lives below the poverty line.
The United States and the European Union have condemned the election as "neither free nor fair".