Officers were called to an alleyway in the 1600 block of Stock Exchange Place, near Sansom Street, around 1:30 a.m. Friday.
According to investigators, the victim said she was in a bar in the 100 block of South 17th Street watching a band.
When the band finished, police say, the woman left through a back entrance on Stock Exchange Place.
That's when, police say, the woman told them she was attacked near some trash bins by 16th Street.
Police say they have interviewed several people but no one has been charged so far.