RSPCA inspectors made the discovery after they were called to a flat in the Beechwood area of Leeds, West Yorkshire, by a cleaning firm last week.
Along with the corpses, the floors throughout the property were lined with around two feet of human and cat faeces.
RSPCA inspector Lynsey Harris, who found the animals, said: "I was horrified by what I discovered. The smell was absolutely sickening. It is unbelievable, but it appears that someone may have been living among these corpses.
"What on earth was going on here?"
She said she found around 100 dead cats, including animals which had been stuffed behind radiators, crammed into a chest freezer and inside an upright fridge freezer - alongside "edible human food".
The discovery was made at the property in Kingsdale Court on Boggart Hill Road in Leeds on September 20.
An RSPCA North spokeswoman said electricity to the property had been turned off for some time and the bodies were in an advanced stage of decomposition, making post mortem examinations impossible.
The spokeswoman said: "We've never come across anything quite as horrific as this.
"There's very little we can do because we don't have a definitive name for who's responsible and we can't tell whether the animals died in the property or were brought in after they'd died.
"It's highly unlikely they died of natural causes, given how they were found, but we can't rule that out so our hands are tied at the moment.
"When we normally go into houses we normally find live animals in a bad way - but to find this number of dead animals is unbelievable."
The RSPCA was contacted by the cleaning firm A-Z Environmental Services, whose staff took 11 large bin liners of bodies and body parts from the property.Reuse content