The cat, which was not micro chipped, had on a blue collar and was found by a member of the public on Tuesday, November 23.
Scottish SPCA inspector Andrew Gray said: “The cat is black and white and appeared to be in good body condition before passing away, with no visible wounds or disease, so it has clearly been someone’s pet until recently.
“We believe the cat had most likely already passed away when it was placed in the bag. We’re keen to find out the cat came to be in this location and the circumstances leading up to its death.
“While we appreciate the death of a pet can be a frightening and upsetting time, this isn’t the correct procedure to follow when dealing with the body of an animal.
If you have any information call 03000 999 999.