One person was killed and seven others wounded in the shooting, according to Philadelphia Police Commissioner Richard Ross.
About 60 people were at the party when gunshots rang out, Ross said.
Ross said four of the victims were teenagers aged 15 to 17 who had been shot in the leg.
An adult victim died from his injuries, while three other adult victims in their twenties were injured in different parts of the body, said Ross.
Ross says the number of fencers involved is unclear and the motive for the shooting is not yet known.