Rare, century-old baseball cards discovered in an Ohio attic have fetched more than US$566,000 at auction.

The cards were from a rare series issued around 1910 and featured Hall of Famers like Ty Cobb and Honus Wagner.

Karl Kissner stumbled upon a wooden box containing hundreds of cards while cleaning out his grandfather’s attic in Defiance, Ohio, last month, but initially had no idea he had discovered what experts are calling the holy grail of baseball card collections.

It wasn’t until a few weeks later, when he had the cards appraised, that Kissner realized the significance of the collection, which was in near-perfect condition.

The whole batch of E98 series cards -- 700 in total -- could be worth millions, experts told Kissner.  

Thirty-seven cards considered to be the jewels of the bunch were expected to garner $500,000 during the National Sports Collectors Convention.

But they exceeded expectations and sold for $566,132 Thursday in Baltimore.

Kissner’s family said it’s evenly dividing the cards and money among 20 members.

The cards belonged to their grandfather, Carl Hench, who once ran a meat market in Defiance and died in the 1940s. His family believes he got the cards as a promotional item from a candy company that gave them out with caramels.

Hench’s house remained in the family until last year, when his daughter died and left everything to her nieces and nephews. 

It took another several months for Kissner to reach the attic in his effort to de-clutter the house -- and come out with a fortune.