Police swarmed the Holloway estate, dispersing party-goers, after reports of a disturbance at 9.49pm.
The 15-year-old male suffered a stab wound to the leg and was taken to hospital where his condition was said to be not life-threatening.
It comes after four youths were wounded when shots were fired at a party in July last year, where nearly 400 youths were celebrating the lifting of an anti-social dispersal order, which was put in place after the brutal murder of 21-year-old Andrew Jaipaul in 2011.
A police spokesperson said: “Officers attended and found a 15-year-old male suffering a stab wound to the leg. He has been taken to hospital where his condition is not life-threatening.
“Police assisted in dispersing those in attendance at the party.
“Enquiries into the assault continue. There have been no arrests at this time.”
Anyone who saw the stabbing, knows those involved or knows where weapons may have been concealed should call Islington CID on 101 or Crimestoppers, anonymously, on 0800 555 111.