The meeting was the first between U.N.investigators and the Syrian leader since the U.N. inquiry opened in June. Brammertz is in charge of the U.N. investigation into the killing of Hariri and 22 others in a truck bombing in Beirut in February 2005.
A U.N. spokesman in Beirut informed reporters that "two separate meetings took place, one with President Assad and one with Vice President Farouq al-Shara." No details from the meetings have been announced.
Syria has battled with political and economic chaos since the release of a U.N. report by Brammertz's predecessor Detlev Mehlis which implicated the Syrian security officials in Hariri's killing and said Syria was impeding the inquiry.
Syria has denied involved in the killing of the former Lebanese premier. Assad recently declared that any Syrian official linked to the assignation will be tried by the Syrian legal system for treason.
The U.N. team made a formal request to interview Assad in January after the defection of Syria's former vice-president, Abdel Halim Khaddam.
Khaddam, who fled to Paris last year, accused Assad of threatening Hariri and of having involvement in his murder.
Assad had declined two previous requests for U.N. interviews but changed his position in March.
Brammertz released a follow-up report in March that lay the groundwork for better cooperation between U.N. and Syrian officials. A few days after the report's release, Assad announced he would meet U.N. commission envoys.
Hariri's assassination sparked massive anti-Syrian protests in Beirut and intensified international pressure on Damascus that eventually forced it to pull its troops and intelligence agents out of Lebanon after 29 years.
U.N. Secretary-General Kofi Annan is trying to form an international tribunal based outside Lebanon to try suspects in the killing. The tribunal has been the focus of discussions since four top Lebanese security officers were arrested in connection with the murder.