The attack happened around 1:30 a.m. on July 18th in the 1500 block of South 13th Street.
Investigators say the female victim was walking when she was grabbed around the waist by an unknown man who sexually assaulted her.
The man was last seen fleeing westbound on Annin Street.
The attacker is described as a Hispanic man, 25-30 years of age standing 5'9" tall. He had a dark complexion, a medium build and was clean-shaven.
He was wearing all black clothing, sneakers and a black Adidas hat with white lettering.
The victim told police the man appeared to be a laborer or a construction worker.
Anyone with information is asked to contact Philadelphia Police at 215-646-TIPS or through phillypolice.com.