Officials with the Pennsylvania Society for the Prevention of Cruelty to Animals said Thursday they went to the house in the city's leafy East Falls neighborhood after receiving a complaint on its cruelty hot line.
SPCA officials said their officers found the remains of several dead cats. They say at least 15 live cats have been seized from the home.
Investigators said the current homeowner is 81-years-old and has lived in the large brick house since 1973. The SPCA said the home was owned by the Academy Award-winning screen legend's mother, Margaret Kelly, until 1970.
Grace Kelly, who was married to Prince Rainier of Monaco, died in 1982 in a car crash.