UN Palestinian refugee agency (UNRWA) spokesman Chris Gunness said 600 food parcels had been delivered to the camp south of Damascus by 1 pm (1100 GMT).
He said there had been "chaotic scenes" as the food was distributed, the first to be delivered to the camp since January 21, when UNRWA took in 138 food parcels.
Syria's state news agency SANA also reported the aid distribution.
"New food aid has entered Yarmuk camp, with the application of a peaceful, popular initiative supported by the Syrian government to alleviate the suffering of the residents surrounded in the camp, taken hostage by armed terrorist groups," it said.
Gunness said UNRWA hoped further convoys would swiftly follow as tens of thousands of civilians were in need.
"We are encouraged by the delivery of this aid and the cooperation of the parties on the ground," he said.
"We hope to continue and increase substantially the amount of aid being delivered because the numbers of those needing assistance is in the tens of thousands, including 18,000 Palestinians, among them women and children."
According to the so-called Syrian Observatory for Human Rights group, at least 86 people have died in Yarmuk in recent months from starvation or lack of medical care.
The camp has been occupied by militants since June, making it nearly impossible for food and medicines to enter or for residents to leave.
Residents have spoken of eating grass, cats and dogs in a bid to stay alive.
The camp began as a home for Palestinian refugees, but long ago evolved into a bustling district housing some 150,000 Palestinians, as well as many Syrians.
But now just an estimated 18,000 Palestinians remain in the camp, much of which has been destroyed in fighting.
SHI/SHI