The joint UN and Syrian Arab Red Crescent convoy comes ahead of planned "assisted departures" from the Rukban camp later this month, UN spokesman Hedinn Halldorsson said.
The five-day mission will "distribute food and nutrition supplies" to 15,000 people, he told AFP, adding that supplies are expected to last 30 days.
"The humanitarian situation in Rukban remains critical, with food being a priority need."
Abu Ahmad al-Dirbas Khalidi, the head of an opposition-run civil council in Rukban, told AFP that "the convoy has entered the camp and aid was distributed to hundreds of families".
Conditions in Rukban are dire, with many surviving on one simple meal a day, often bread and olive oil or yoghurt, according to one resident.
Neighbouring Jordan has largely sealed its border since 2016 following a deadly attack against its soldiers, claimed by the Islamic State group.
Aid deliveries from regime-held areas to the camp, which lies in a region where US-backed rebels are present, requires permission from Damascus.
The latest aid delivery is the second part of a three-phase process, Halldorsson said.
"The first phase of the operation was a needs assessment mission in late August," he said.
"The third phase, later this month, will be assisted departures" for between four and six thousand people who wish to leave Rukban, he said.
The UN and SARC sent a mission to the camp last month to determine how many people remained inside and who wanted to leave, the UN said last week.
Some 47 percent of surveyed camp residents said they wanted to stay, citing reasons including "security concerns" and "fear of detention", the UN said.
Rights groups have warned that civilians returning to government-held territory have faced detention and conscription.
The Syrian government and its key backer Russia said in February they had opened corridors out of the camp, calling on residents to leave.
More than half of the original population has left in the past months, the UN says.
In February, a humanitarian convoy of 133 trucks delivered food, clothes, healthcare items and medical supplies to the camp's residents.
The February 6 delivery was only the second in three months.
Syria's civil war has killed more than 370,000 people and displaced millions since it started with the brutal repression of anti-government protests in 2011.