Robert Gray of Portscatho, Cornwall, who owns a bed and breakfast took the ancient artifact in his attic for an x-ray, where images revealed the outline of a perfectly preserved ancient cat - complete with face, ears, spine and brain.
Gray, 56, said the object had belonged to his late father Peter Gray who was an Egyptologist.
But he had never realised the cat was a genuine piece of history and is worth several thousand pounds, the 'Daily Mail' reported.
"My father acquired the cat in the 1970s as a token of thanks from a museum. It's been in the loft languishing there for 50 years," Gray said.
"It's perfectly bandaged up and a very interesting item. Apparently interior designers love this sort of thing, as ghoulish as it sounds," Gray added.
"It could fetch a couple of thousands pounds but I will probably donate it to a museum," he said.
Experts at the Royal Cornwall Museum have now verified the remarkable find.
Ancient Egyptians mummified animals as religious offerings or to ensure their beloved companions would follow them into the afterlife.
Gray said his research has suggested that often the mummies would be a fake.
"You went to the mummifiers and said you wanted to send goodwill to the afterlife but some would take your money and stuff a bunch of rags inside," Gray said.
Cats were particularly popular subjects during the Ptolemaic period from 305 BC to 30BC because they were believed to represent the war goddess Bastet.
X-ray images of the mummified cat show the neck is still intact, suggesting it was a prized pet rather than a sacrifice to the gods.
"It was very exciting to see the X-ray. It's a lovely face and the wrapping is very good. It's been very well kept," Jane Marley, curator of archaeology and world culture at Royal Cornwall Museum, said.