The volunteers said on Wednesday they plan to join up with 200 other recruits on their way to the Turkish border.
Amir Jalilinejad, chairman of the Student Justice Movement, a group that helped recruit the fighters, said "We are just the first wave of Islamic warriors from Iran.
"More will come from here and other Muslim nations around the world. Hezbollah needs our help."
The volunteers hope to cross into Syria from Turkey and then make their way to Lebanon.
Organisers said the group are carrying no weapons, and it was unclear whether Turkey would allow them to cross the border.
Other volunteers, such as 72-year-old Hasan Honavi, have combat experience from the 1980-88 war with Iraq.
"God made this decision for me," said Honavi, a grandfather and one of the oldest volunteers.
"I still have fight left in me for a holy war."
The group, chanting and marching in formation, assembled in a part of Tehran's main cemetery that is reserved for war dead and other "martyrs."
Some bowed before a memorial to Hezbollah-linked suicide bombers who carried out the 1983 bombing of a US army base in Beirut that killed 241 US servicemen.
Iran insists it is not directly involved in the conflict on the military side, although it remains a key ally of Hezbollah.
"We cannot stand by and watch out Hezbollah brothers fight alone," said 21-year-old Komeil Baradaran.
"If we are to die in Lebanon, then we will go to heaven. It is our duty as Muslims to fight."