Police were called around 12:30 a.m. Friday to the 2300 block of South 20th Street for the report of a stabbing.
Officers entered the home and found the 64-year-old victim lying on her back in a second-floor hallway outside a bedroom.
Police say she was unresponsive and bleeding. A knife, described as a "bread knife" with a 10 or 12-inch blade, was located a foot away from her head, police say. There was blood on the knife.
"She was clearly stabbed several times in her neck," Philadelphia Police Chief Inspector Scott Small said.
Police say the woman lived in the home. Several family members were inside at the time and were being questioned by detectives as witnesses.
One family member, a 16-year-old male who had blood and cuts on his hands, was taken to Jefferson Methodist Hospital. He is considered a person of interest, police say.
Small says police believe he also lives in the home.
His exact relationship to the victim is not yet clear.
"We don't know what motivated this stabbing that escalated and turned into a homicide," Small said.
Investigators were working to obtain a search warrant for the home.
Small says there are surveillance cameras in the block and police are looking to see if they captured anything outside the home to help in the investigation.