The charity issued a stark warning after the cat was found in a homemade snare in a North Staffordshire garden.
A homeowner discovered the animal in his garden in Werrington and found the device was cutting into the cat's neck.
The snare was cut to relieve some of the pain to the cat.
The RSPCA went to the scene on October 17 and discovered deep cuts and scabs around the elderly cat's neck - they also found an untreated cancer.
The underweight and dehydrated cat was rushed to the vets but, because of her neck wounds and various medical conditions, the vet decided the best option would be to put the cat to sleep.
Type of snare
Illegal
Where
Werrington, North Staffordshire
When
October 2020