All seven of the JK Rowling books are available to rent free of charge through the subscription service.
"Nowhere else can customers borrow any of the seven Harry Potter books for free, with an unlimited supply of each title and no waiting list," said Russ Grandinetti, vice president, Kindle Content.
"A $79 Prime membership was already the best deal in retail, and now it's become even more valuable."
The Kindle Owners' Lending Library, launched back in January, allows subscribers to borrow one book per month with no due dates. More than 145,000 are available to rent free of charge.
Prime members can also take advantage of free two-day shipping on millions of items from the online retailer, as well as unlimited streaming of more than 18,000 movies and TV episodes.
The Harry Potter series was added to the library following a licensing agreement between Amazon and JK Rowling's Pottermore.