Antonio Guterres toured the camp in Arsal village in northeast Lebanon, meeting some of the refugees who are living there.
He said the number of Syrian refugees in Lebanon compared to the Lebanese population as a whole was the equivalent of 56 million refugees entering the United States.
The UNHCR said in a report on Friday that a growing number of Syrian refugee children in Lebanon and Jordan are fast becoming primary providers for families who lack resources for basic survival.
More than two million Syrians have fled their homes because of the country's raging conflict, seeking shelter in neighboring countries such as Jordan, Lebanon, Turkey and Iraq.
At least half of the refugees, 1.1 million, are children.
Of those, some 75 percent are under the age of 12, the UNHCR report said. AP To watch Raneem Bou Khzam's report, please click on the VIDEO above