The incident occurred at 31st and Spring Garden streets in Powelton.
Around 1:00 p.m. Wednesday, the suspect and his ex-girlfriend left a drug recovery program about a block away from the scene.
As the two approached The Caring Center, police say the suspect pinned the woman against the front door and repeatedly stabbed her in the chest and stomach.
"He obviously looked like he was angry. She was cowering and crying, saying 'no, no, no.' So I stopped the car, honked the horn, jumped out, ran across the street, and saw that he was hitting her. Then I saw she had red marks on her white t-shirt," witness Terry Bosworth said.
The suspect fled on foot down Spring Garden towards the Art Museum. Though he tried to ditch the knife, police say they have recovered weapon.
The suspect was apprehended a short time later with the help of witnesses, police say.
The 26-year-old victim was transported to the Hospital of the University of Pennsylvania in critical condition.
No children were affected in this incident.