The fantasy tale, Mr Tumpy's Caravan, was among a collection of Blyton manuscripts bought at auction in September by the Seven Stories children's book centre in Newcastle, northern England.
Its title is similar to that of a published book, Mr Tumpy And His Caravan, but the Enid Blyton Centre has confirmed it is a previously unpublished work.
Blyton died in 1968 after writing almost 800 books, including the Famous Five series and Faraway Tree series. She has sold more than 500 million books worldwide.
The Famous Five books of the 1940s and 50s follow Julian, Dick, Anne and George and Timmy the dog as they foil kidnappers and smugglers aided by 'lashings' of ginger beer and cream buns.
Critics have long branded her books sexist, racist and overly simplistic, but Blyton's stories remain hugely popular, selling more than 10 million copies a year.
