It happened just before 6 a.m. on Friday inside a home on the 600 block of Franklin Place.
According to police, a 31-year-old woman and a 33-year-old man got into a verbal altercation when the man tried to assault the woman.
Police say the woman then grabbed a knife and stabbed the man in the chest. The man grabbed the knife back and stabbed the woman in the thigh.
Both were taken to Thomas Jefferson University Hospital.
The woman is listed in stable condition. The man is currently listed in critical condition.
Their identities have not been released.
No arrests have been made, and no charges have been filed.
The incident remains under investigation.