David Richardson, 76, said he picked up the canine, Bella, from an animal shelter in about 1982, at least three years after she was born, The Telegraph reported Thursday.
Richardson's claims make Bella an astonishing 200-years old in dog years.
"I'm convinced she is the oldest dog in the world," Richardson said.
The Royal Society for the Prevention of Cruelty to Animals said it cannot find documentation about Bella which is required by the Guinness World Records to confirm a claim.
"Unless we can (obtain) a doggy birth certificate or some really clear evidence from the RSPCA then we won't be able to prove Bella's age and we can't list her as the oldest dog," Guinness manager Gareth Deaves said.